In most categories condition is the whole description. Here it is half, and the two halves must not be blended.
Two statements, kept apart
Condition — what the object looks like now. Provenance — where it came from and what you can show.
A listing that says "excellent condition, authentic signature" has smuggled a claim about provenance inside a claim about condition. That is the sentence that becomes a dispute.
Condition language
Shirts and kit — pilling, staining, sweat marks, pulled threads, cracked print, lifted numbers or badges, whether it has been washed. Equipment — face and edge damage, repairs, re-gripping, whether it has been used. Paper — creases, tears, pinholes, foxing, fading. Frames — glass condition, mount, whether the item has been fixed down and how.
Fading of a signature is condition
Say it plainly, say where it is worst, and photograph in neutral light rather than warm light, which flatters ink.
Provenance language
Say which rung you are on and nothing more: present at the signing with a photograph, obtained at a known event, certificate from a named issuer, bought from a previous owner, or unverified.
Washing and restoration
A washed match-worn shirt is a different object from an unwashed one. A repaired tear, a replaced badge, a re-stitched number — all declared, always.
Questions people ask
Does a stain lower the value of a match-worn shirt?
Sometimes it raises it, because it is evidence of use. Describe it rather than apologising for it.
How do I describe an unidentified signature?
As unidentified. "One signature I cannot identify" is a perfectly good line.
Can I say "looks genuine to me"?
Yes, because it is plainly an opinion. The problem is only ever an opinion dressed as a fact.
More: condition words across every category, describing cricket memorabilia.