Vintagedegu,
A legitimate appraiser of high end art, ala million dollar Rembrandt, would/should be confident of the authenticity before giving appraisal. Either he/she would be an expert or would get the opinion of a reliable expert. The item may already come with strong documentation and provenance (ala receipt and catalog from purchase at Sotheby's). She may not be personally and financially guaranteeing the authenticity, but she would confident in it. It goes without saying that there is a value difference between original Rembrandt painting and a 1977 copy.
It's in stuff like home appraisal where they won't/can't authenticate the whole contents. A family might own T206s, autographs, lamps, tables and chairs, figurines, game used jersey, inexpensive paintings etc and no one person is an expert in all that. The appraiser just reviews the stuff, look at LOAs and receipts when deemed necessary and gives an overall value. The appraiser is basically an official documenter. Though if, in the process, he comes across something that he knows is fake or a reprint, he will value it at as a fake or a reprint. Just don't expect a home contents appraiser to sit down with a microscope and black light to authenticate each hockey card in Bobby's shoe box, before going off to authenticate mom's antique perfume bottle collection and dad's box of vintage car parts.
I make no comment on the eBay Picasso painting, other than to note is was being sold as "attributed to Picasso" and "this art piece is sold as attributed/manor of Picasso." The seller doesn't say doesn't say it is "by Picasso." It appears even the seller isn't convinced by the accompanying documentation
