Reasonable request?

[thecatspajamas]

I agree that your liability should only be for the cost of the ball (and if sold on eBay, that will extend to the cost of shipping as well if they file a claim).

One thing to be aware of though: Some potential buyers will use a statement like that as a sort of backwards way of suggesting you take another look at the signature and be sure yourself that it's authentic.

Personally, I would rather they just come right out and say, "are you sure it's authentic, because I don't think it is, and here's why" than to give a laundry list of fees they could stack up to prove its not authentic and expect you to reimburse them for, presumably to scare you into taking another look at it. Some feel that the indirect approach gets better results though.

Whatever the case, talk it through with the buyer. Actually engaging in conversation with them will ease their minds more than a terse response, and you may find that they are simply reacting to some other situation where they got burned.