Not sure which is my best... probably a brand new dvd set worth over $100, which I scored on ebay for $32.
Worst would have to be the two times I received fakes... one was a burberry scarf, which I paid $47 for, and it's just sitting in my closet. Another one was a pair of Seven Jeans for $65, but I got my money back. This was more than 3 years ago, and I've since been more careful and thankful that there are forums like tpf that help authenticate!