Link building is one of the easiest SEO services to sell badly, because the deliverable (a number of links) is easy to promise and the quality of that deliverable is hard for a buyer to evaluate without SEO expertise of their own. Vetting an agency well means asking questions most sales conversations are designed to glide past.
The disclosure test
Before signing anything, ask directly: what kinds of sites will links come from, and what's the actual process for securing them? A reputable agency running legitimate outreach, digital PR, or content-driven link acquisition can answer this in specific terms — the types of sites they target, roughly what tactics they use, how they identify prospects. An agency that answers only in vague marketing language ("high-authority outreach," "premium placements," "white-hat strategies") without specifics is very often obscuring a process that wouldn't hold up to scrutiny — private blog networks, paid link schemes, or low-quality guest post farms dressed up in legitimate-sounding language.
This is the single highest-value question in the whole vetting process, because a legitimate agency has no reason to be vague about it, and an agency running a scheme has every reason to be.
Ask for real examples, not case study screenshots
Request a sample of live, currently active links the agency has placed for existing clients, ideally in a comparable industry. Visit the sites yourself. Check whether the linking page has genuine content and traffic, or reads as a thin site that exists primarily to sell links. A reputable agency can usually share several real examples without much friction; an agency relying on low-quality tactics is often reluctant, offers only anonymized screenshots instead of live URLs, or provides examples that turn out on inspection to be thin, low-relevance placements.
Don't trust domain metrics alone
Third-party domain authority-style scores are useful as one input, but they're also the metric most directly targeted by manipulation — link farms and private blog networks are frequently built specifically to inflate these scores, since they're what buyers commonly check first. A site with an impressive-looking authority score but no genuine topical relevance to your industry, minimal real traffic, or content that reads as filler is a worse link than a lower-scored site with real relevance and an actual audience. Weight relevance and genuine engagement at least as heavily as the metric itself.
Structure a trial before a long-term commitment
Rather than signing a 12-month retainer upfront, propose a 2-3 month trial with a modest, clearly defined number of links to be delivered. This is long enough to genuinely evaluate the agency's process and the quality of what they deliver, and short enough that a poor fit doesn't cost a full year of budget before you find out. During the trial, check delivered links against what was promised — both in volume and in the quality signals discussed above — before deciding whether to extend.
Be wary of volume-based pricing
A pricing model built purely around the number of links delivered per month, with no quality or relevance criteria built into the agreement, incentivizes exactly the wrong behavior: it rewards the agency for hitting a link count, not for placements that are actually relevant and valuable. Pricing tied to outcomes, project scope, or a defined process with quality benchmarks built in aligns incentives better than a straightforward per-link or per-month volume rate. If volume-based pricing is the only structure offered, treat it as a signal worth weighing alongside everything else, not a dealbreaker on its own — but combined with vagueness about sources, it's a meaningfully worse sign than either alone.
