In the broadest category on the site, one question does most of the work.
The question
"What makes this one different from an ordinary one?"
Edition, run, variant, year, marking, provenance. A seller who answers precisely knows the object. A seller who answers "it's rare" has told you nothing you can check.
Then
"What is the edition size?" A number is a fact. "Rare" is a claim.
"Is it an original issue or a later reproduction, and how do you know?" Both are sellable. Only silence is a problem.
"Can you show every face of the box?" Where the packaging is part of the value — which it usually is — the back and the bottom carry the wear.
"Can you lay out everything that comes with it?" Certificates, inserts, stands. Count rather than trust.
"Who issued the certificate?" It is worth its issuer's reputation and nothing more.
"How certain are you about what this is?" An honest "I believe, but cannot confirm" is worth more than confidence, and should be priced lower.
What protection covers
A reproduction sold as original, missing pieces described as present, damage not shown, or a different item than the one on camera: seven days from delivery.
Questions people ask
Is a numbered edition always worth more?
Not if the edition is large. Ask the size, not just the number.
Does the box really matter?
For anything issued boxed, often more than the object.
What if nobody can identify it?
Then bid what it is worth to you as an unidentified object.
More: buying collectibles, what one is worth.