[Directly]

1) I would ask the seller to remove the photo for a look & see
A) if they say no, ask why?--I would think if its right the seller would will be cooperative to your request
B) Advise you are more than willing to pay to have the picture
professional backed at any frame shop of his choice.

2) If he says No--I would pass or bid the amount I was comfortable with paying, but if you really like it who cares.
A refund in writing is OK, but could be worth only the paper its written on.

3) If he allows, look for a Photographers name or location of the Studio. Although many photos of this size or not marked this could help.

4) Pay strict attention to the overall condition, especially the back, the mounting card board edges, the photo's edges & surface, etc. If all the prints medium looks too good to perfect condition, I would question its age.

5) I was offered several old Cabinet Cards where the old original photo had either been scrapped off or covered over with new reproduction Indian Chief's photo's. The photo's white edge's & cut & especially the photographs grainy surface gave it away for me.

Another example: I once inspected several Cabinet card's with Annie Oakley image. In this case the complete Cabinet Card was reproduced. --The dead giveaway was inspecting the extreme edge of the photograph's condition which was snow white with a near perfect straight cut. Also overall the Cabinet Card was in perfect condition??

7) I should add we have all seen paper items that were artificially aged.

8) Only my opinion of a few things I would check if I wanted the photo. Good Luck!