Auction lemons
I have bought many F2s from on-line auctions, for my collection and for spare parts. Most of the F2s I bought were about as described, gradings were nearly always lower than stated (eg mint were never really mint) and a few turned out to be real lemons.

The F2AS below looked quite nice and was sold as is. However, the listing did not state it was dropped in salt water and everything was rusted solid. I complaint and the seller refunded half the purchase price because he genuinely did not know it was so bad. However, I had some really bad experiences when I complaint, and Paypal would not help when there's a quality dispute. So be careful when you buy anything unseen.
Original photo from eBay auction Original photo from eBay auction
Inside the camera was full of rust There wasn't much I could salvage