I, personally, am always wary about buying autographed items just because, you never know. I did buy one item, an original Star Wars LP, for $25, signed by Dave Prowse, Peter Cushing, and Mark Hamill. I had autographed items from two out of three in my collection already (the Prowse I had from the 10th anniversary convention, the Mark Hamill from a friend who caught up with him during a Disney-MGM Studios "Star of the Day" appearance), and those two looked authentic. The guy I bought it from had the story that his dad had worked on the film, but his parents were divorced and he threw the album in the back of a closet for years (and it looked it). But, I took the chance on that one. All my other autographs I've gotten in person at conventions (except that Mark Hamill I mentioned). I think there's something nice about an autograph as a memento of actually meeting the person, too.
Auriette