Yard Seller: "Yeah, I dunno. It says 'Leica M3' on it but it doesn't have a red dot so it's probably not real. $25 too much for you?"
True story:
Some years ago, my boss came to me and said, "A family friend just passed away and his wife is looking for help selling his cameras, and will offer you a deal if you take the whole thing off her hands."
A couple days later, he show ups with an absolutely mint/like new assortment that included an M6, with a 50mm Noctilux, as well as another 50mm, 28mm, and 90mm lenses as I recall - all Leica.
Told them what the stuff was worth - as I recall it was something like $10K (or more) at the time. The lady offered it to me for $5K and I stupidly declined. I just didn't want to tie up that much money in a 35mm system.
So, I had my shot at the "Leica find" deal and blew it ;(
(In fairness, this was years before I contracted the Leica GAS disease...)