How to Vet an SEO Agency: A Practical Checklist for Technical Audits, On-Page Optimization & Core Web Vitals

You’ve just sat through a pitch from an SEO agency. They threw around terms like “crawl budget optimization,” “LCP reduction,” and “intent mapping.” They showed you a mock dashboard with green arrows pointing up. It sounded great—but now you’re left wondering: How do I actually check if they know what they’re doing?

Hiring an SEO agency is a bit like hiring a mechanic for a car you can’t lift the hood on. You need a checklist—not just of services, but of how those services should be delivered. This guide walks you through the core offerings of a professional SEO agency: technical audits, on-page optimization, and Core Web Vitals. We’ll cover what each service should include, what red flags to watch for, and how to brief the agency so you get measurable work, not just promises.

1. The Technical SEO Audit: What a Real Crawl Analysis Looks Like

A technical SEO audit is the foundation. Without it, any on-page or content work is guesswork. A proper audit examines how search engines discover, crawl, and index your site. It’s not a one-page PDF with five bullet points; it’s a structured investigation.

What the Audit Should Cover

• Crawlability & Indexation: The agency should check your `robots.txt` file for accidental blocks, review your XML sitemap for errors (orphaned pages, missing URLs), and analyze your internal link structure. They should tell you if important pages are being left out of the index.
• Crawl Budget: For larger sites (10,000+ pages), the agency should assess how Googlebot spends its crawl budget. Are low-value pages (tag pages, filtered category pages, thin affiliate content) eating up the budget? They should recommend consolidating or noindexing those.
• Duplicate Content & Canonicalization: A thorough audit includes a scan for duplicate content—same product descriptions across multiple URLs, HTTP/HTTPS versions, or www/non-www conflicts. They should check your canonical tags for correct implementation and flag any pages where the canonical points to the wrong URL.
• Site Structure & URL Hierarchy: The audit should map your site’s architecture. Are your most important pages three clicks from the homepage? Are there broken internal links? A good agency will provide a visual or tabular breakdown of your site’s depth.
• Core Web Vitals Baseline: This is non-negotiable. The audit must include current LCP (Largest Contentful Paint), FID/INP (First Input Delay / Interaction to Next Paint), and CLS (Cumulative Layout Shift) scores. If they don’t mention Core Web Vitals in the audit scope, ask why.

Red Flags in an Audit

• “Your site is perfect” – No site is perfect. If the agency hands you a clean report, they probably ran a shallow scan.
• “We’ll fix everything in two weeks” – Technical SEO fixes often require development sprints, content changes, and redirect mapping. Realistic timelines are 4–8 weeks for initial fixes.
• “We guarantee first-page ranking” – This is impossible. Search engines control rankings. Any agency promising this is either lying or using black-hat tactics.

How to Brief the Audit

When you brief the agency, provide:

• Access to Google Search Console and Google Analytics (read-only is fine).
• A list of your top 20–50 priority pages (the ones that drive revenue or traffic).
• Any known issues (e.g., “Our blog pages don’t index,” “We recently migrated from HTTP to HTTPS”).
• Your current Core Web Vitals scores if you have them.

2. On-Page Optimization & Content Strategy: Beyond Keyword Stuffing

On-page optimization has evolved. It’s no longer about shoving “cheap running shoes” into the title tag 12 times. Modern on-page SEO focuses on relevance, structure, and user experience.

The On-Page Checklist

• Keyword Research & Intent Mapping: The agency should start with keyword research, but not just volume. They need to map keywords to search intent: informational (“how to clean leather shoes”), navigational (“Nike size chart”), commercial (“best running shoes for flat feet”), and transactional (“buy men’s trail running shoes”). Each page should target one primary intent.
• Content Strategy & Gap Analysis: A good agency will audit your existing content against what your competitors rank for. They’ll identify content gaps—topics you haven’t covered that your audience searches for. They should present a content calendar with topics, target keywords, and estimated effort.
• On-Page Elements: For each page, they should optimize:
• Title tag (unique, includes primary keyword, under 60 characters)
• Meta description (compelling, includes call-to-action, under 160 characters)
• H1 and H2 structure (logical hierarchy, keyword placement in H1)
• Image alt text (descriptive, not keyword-stuffed)
• Internal linking (links to relevant pages with descriptive anchor text)
• Content Quality & E-E-A-T: For YMYL (Your Money or Your Life) topics, the agency should emphasize Experience, Expertise, Authoritativeness, and Trustworthiness. This means citing sources, including author bios, and avoiding thin or AI-generated content without human oversight.

Risk-Aware Content Practices

• Avoid Black-Hat Tactics: The agency should never use:
• Keyword stuffing in hidden text or low-quality paragraphs.
• Auto-generated content (unless clearly labeled and useful).
• Cloaking (showing different content to users vs. search engines).
• Beware of Over-Optimization: If every page has the exact same keyword density or structure, Google may flag it as unnatural. The agency should vary content length, tone, and formatting.
• No Guaranteed Rankings: Any agency that says “this content will rank #1 for ‘best SEO tools’” is misleading you. Rankings depend on competition, backlinks, and algorithm updates.

How to Brief On-Page Work

• Provide your brand voice guidelines and any existing content.
• Share competitor URLs you admire (or want to beat).
• Specify if you have a content management system (CMS) restriction (e.g., no custom fields, limited HTML access).
• Ask for a sample optimized page before they do 50.

3. Core Web Vitals & Site Performance: The Technical Foundation

Core Web Vitals are now a ranking factor. If your site loads slowly, shifts layout, or doesn’t respond to user input, you’ll lose visibility—regardless of how good your content is.

What the Agency Should Do

• Measure Field Data: The agency should pull real-user data from Google Search Console (the “Core Web Vitals” report) and Chrome User Experience Report (CrUX). Lab data (from Lighthouse or PageSpeed Insights) is useful for debugging, but field data reflects actual user experience.
• Identify Bottlenecks: Common issues include:
• LCP: Slow server response time, render-blocking resources, large images.
• CLS: Ads or images without dimensions, dynamic content injection (e.g., cookie banners, popups).
• INP/FID: Long tasks from heavy JavaScript, third-party scripts (analytics, chatbots, social widgets).
• Provide a Fix Roadmap: The agency should not just list problems—they should prioritize fixes by impact and effort. For example:
• Critical: Optimize hero image (reduce LCP by 0.8s).
• High: Set explicit width/height on ad slots (fix CLS).
• Medium: Defer non-critical JavaScript (improve INP).
• Test & Validate: After fixes are implemented, the agency should re-run tests and compare before/after scores.

What Can Go Wrong

• Wrong Redirects: If the agency sets up 302 (temporary) redirects instead of 301 (permanent) for moved pages, you lose link equity. If they chain redirects (A → B → C), you slow down the page and dilute authority.
• Aggressive Image Compression: Over-compressing images can ruin visual quality. The agency should balance file size with acceptable quality (e.g., WebP format with 80% quality).
• Removing Third-Party Scripts Blindly: Some scripts (analytics, payment gateways) are essential. The agency should suggest async loading or deferral, not outright removal.

How to Brief Performance Work

• Share your current PageSpeed Insights URLs (both mobile and desktop).
• Provide a list of third-party scripts you require (e.g., Google Analytics, Hotjar, Facebook Pixel).
• Specify if you have a development team that can implement code changes, or if the agency must work within a CMS (e.g., WordPress plugin constraints).

4. Link Building: The Riskiest Service to Brief

Link building is where most SEO agencies go wrong. Black-hat tactics (private blog networks, paid links, automated outreach) can trigger manual penalties. A reputable agency will be transparent about their methods.

What Ethical Link Building Looks Like

• Content-Driven Outreach: The agency creates genuinely useful content (guides, original research, infographics) and pitches it to relevant sites. They don’t pay for links; they earn them.
• Digital PR & Brand Mentions: They find unlinked brand mentions and request conversion to links. They also pitch stories to journalists and bloggers.
• Competitor Backlink Analysis: They analyze your competitors’ backlink profiles (using tools like Ahrefs or Majestic) and identify linkable assets you can replicate.
• Relevance Over Quantity: 10 links from industry-relevant, high-authority sites are worth more than 100 links from random directories or spammy forums.

Red Flags in Link Building

• “We can get you 100 links in a month” – Unless you have a massive news story, this is almost certainly spammy.
• “We have relationships with major publishers” – Ask for examples. If they can’t name specific sites (anonymized), be skeptical.
• “We use private blog networks” – PBNs violate Google’s guidelines and can get your site penalized.
• “We guarantee a boost in Domain Authority” – DA is a third-party metric, not a Google ranking factor. It can be manipulated.

How to Brief Link Building

• Specify your niche and the types of sites you consider relevant.
• Provide a list of your current backlinks (export from Search Console or Ahrefs).
• State your risk tolerance: “I’d rather have 5 high-quality links per month than 50 low-quality ones.”
• Ask for a sample outreach email before they start.

5. Analytics & Reporting: What to Expect (and What to Ignore)

Reporting is where agencies often hide behind vanity metrics. You need to know what to look for.

Metrics That Matter

• Organic Traffic (by landing page): Are your priority pages getting more visits?
• Keyword Rankings (by intent): Are you ranking for commercial/transactional terms, not just informational?
• Conversion Rate (from organic): Are visitors taking desired actions (purchases, sign-ups, calls)?
• Core Web Vitals Scores (month-over-month): Are performance metrics improving?
• Backlink Quality (new referring domains, not total links): Are you gaining links from relevant, authoritative sites?

Metrics to Ignore (or Question)

• Domain Authority (DA): It’s a third-party metric, not used by Google. An agency obsessed with DA may be gaming the system.
• Total Backlinks Count: 10,000 spammy links are worse than 200 quality links.
• Pageviews (without context): A spike in pageviews from low-value pages doesn’t help your business.

Reporting Red Flags

• “We’re working on it” without specifics – If they can’t show what they’ve done this month, they’re probably not doing much.
• Screenshots of Google Search Console without analysis – A report should interpret the data, not just present it.
• “Rankings dropped due to Google update” – While algorithm updates happen, a good agency will identify why your site was affected and what to do about it.

6. The Final Checklist: How to Choose (or Fire) an SEO Agency

Before you sign a contract, run through this checklist:

If an agency can’t answer these questions clearly, or if they dodge with jargon, walk away. A good SEO agency will welcome scrutiny—because they know their work is solid.

Summary: Your Role as the Client

You don’t need to be an SEO expert to hire one. But you do need to know what questions to ask. Focus on process over promises. A reputable agency will show you their audit methodology, their content workflow, and their performance benchmarks. They’ll be honest about risks—including the risks of black-hat links, wrong redirects, and poor Core Web Vitals.

And remember: SEO is a long game. If an agency promises overnight results, they’re selling snake oil. If they show you a detailed, transparent plan with realistic timelines, you’ve found a partner worth working with.

Next steps: Learn how to brief a technical SEO audit or read about on-page optimization best practices.