[thecatspajamas]

It's a tough call, but it sounds like you need to leave out the LOA part of it and treat it like a museum curator might handle Joe Schmoe bringing an item of interest in for examination. No write-ups, just a "here's what I have, what is it?" service, with the final report being verbal rather than written. I'm not sure that would affect insurance/liability while the item is in your posession, but would definitely eliminate a lot of shady submissions intended to dupe you into giving a false thumbs-up for the purpose of re-selling, and for the most part would narrow your customers down to those who are genuinely interested in the piece itself and in hearing what you have to say on it rather than just looking for documentation for flipping it on eBay.

As far as a fee structure (since your time is valuable), maybe a flat submission fee plus some hourly rate if the amount of research required and the submitter's desire for further knowledge on the piece exceeds some predetermined time frame.

Not to lump you into the same category, but I'm picturing something more like the museum director, Mark Hall-Patton, who makes appearances on Pawn Stars (long beard, Amish-style hat). I don't know if he is paid for his appearances (surely), but he comes in, gives his analysis of the item and tells some of the history of it, and he's out. No evaluation of "value," no written documentation, just straight expert opinion. Whether that opinion satisfies the curious itch of the owner, or proves to him that he has mistakenly purchased a fake wouldn't change the evaluation.

Just some more thoughts to add to the mulling pot.