for what its worth: I work in retail and this thing happens alot. I sold a guy the nicest Kenwood car audio cd player we had. He said he was taking it elsewhere to have it installed. He returned about a half hour later saying that he got the wrong deck. I openned the box and found a 2 year old, bottom of the line kenwood deck. Now I know that the box I sold him was the right one (we had just gotten them in) but there was nothing I could do but refund him his money and take a $400 hit.
Another time a guy bought the top of the line Denon home receiver and returned it the same day unopenned (or so we thought.) A couple weeks later, a guy buys the same receiver, but comes back later in the day saying he got the wrong one. There was an ancient JVC receiver in the box. Which customer was scamming??? No way to tell.
People scam, other people get shafted because of it. It should be the store manager's call on what to do with your uncle's camera. Be polite and respectful and ask him to help you out, dont demand anything. Its his call 100% since you cant prove that you didnt switch the cameras, remember that when you are talking to him.