Checking a certificate
Free, and it always will be. A certificate nobody can check is a private note.
Somebody gave you a certificate identifier — it looks like adid_ followed by thirty-two characters — and you want to know whether it's real. That's what /verify is for, and it costs nothing, for anyone, always.
What it tells you
Whether the certificate exists, the registered name it was issued to, and whether it's current. That's the whole free tier, and it's intentionally narrow.
What it does not tell you
It does not return a grade or a dossier — those are a judgement about a company, and handing one to whoever merely knows an identifier would be a different act from confirming a certificate is valid. The holder releases those — see sharing your grade and dossier — one counterparty at a time.
It also will not tell you whether a company is certified in general. There is no directory — this resolves the one identifier you were handed, and nothing else. A searchable list of who is verified would be competitive intelligence about our customers.
A wrong identifier and a real-but-unknown one look the same
If what you typed doesn't resolve, the page says so the same way whether the identifier was mistyped or never existed at all. That's deliberate: answering the two cases differently would let this page be used to fish for which identifiers are real, one guess at a time.
A holder can also give you a link directly — /verify/<identifier> resolves the same result without you typing anything, which is what a badge on somebody's site links to.