I'd be interested to have you elaborate in this just a bit, if you didn't mind.

Why would you bid on an item if you had any doubts?

As a collector, does a 3rd party authentication matter?

Now, just my side of that is I don't plan on selling much so a 3rd party "guess" doesn't effect me at all.

For what it's worth, 3rd parties are just that. You either saw it signed or you didn't, it's that simple because that's the only way to know for sure. Anything else is pure speculation, and what matters most is YOURS because its in your collection.

If its something you wanted in your collection, I'd ask you reconsider your stance, especially if its a unique item.

I had a eBay buyer go to a 3rd party who will remain nameless. They returned the item as "not likely genuine". However, the clincher is quite simple. The athlete in question I've worked with for 5 years. I've got a stack of 50 blank 8x10s, all signed.

When I contacted the authenticator I asked them about the "exemplar" they were using? Zero response. I ended up getting the athlete to write a letter to the buyer citing the authenticity of the signature. He advised me he tried to forward that letter to the vendor and demand a refund. They canned him a response saying you pay for an opinion and that's what you got.

After all that, the buyer finally let it go and kept the piece. Meanwhile a credible authentication "company" was confronted by an agent for an athlete and did zero about it.