There is no condition scale here, and there is something more important to get right first.
Condition and provenance are separate
Condition is what the object looks like now. Provenance is where it came from and what you can show.
A listing that says "excellent condition, authentic signature" has smuggled a claim about origin inside a claim about appearance. That is the sentence that becomes a dispute. Two sentences, always. Describing memorabilia.
Condition language
Shirts and kit — pilling, staining, sweat marks, pulled threads, cracked print, lifted numbers or badges, and 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, how the item is fixed down.
A faded signature is a condition fact. Say where it is faded worst, and photograph in neutral light.
The provenance ladder
Strongest first: present at the signing with a photograph · obtained at a known event with details · a certificate from a named issuer · bought from a previous owner who said so · unverified, sold as seen.
None of those is shameful. Being vague about which one is.
Certification is not grading
Some services authenticate signatures. That is an opinion about origin from a named party — not a condition grade, and worth exactly that party's reputation.
Questions people ask
Does a stain lower the grade?
On a match-worn shirt it often raises the value. Describe it.
Can Metzee authenticate?
Is "authentic" a grade?
It is a guarantee, and one most sellers cannot support.
More: buying memorabilia, provenance.