I've only had a couple of buying issues. One, last year, was where this lady canceled the auction after I won claiming that she didn't have it, then relisted it. So I wasn't out anything, but it was annoying.
The second was where I bought a Radiata Stories poster from some guy. Took him forever to ship it, he finally apologized & said he was going to send me some extra stuff to make up for it. The poster finally arrived not in a tube but rolled up & put diagonally in a box...so you can imagine that something was sat on the box at some point creasing the poster in the middle of the roll - so right down the middle. :| He refunded me, but I was more upset at the loss of the poster since no one else had it listed.
EDIT: on the flip side, I had a very good experience last year. Bought the first Ar Tonelico from some lady who said her ex had left all his games with her & told her to do whatever she wanted with them. Used a buy it now & got a very good price on it. Before she shipped I contacted her & told her that I had noticed the second game in the background of one of her photos but didn't see it listed, and asked if she was going to be selling it (it also didn't show as a sold listing by her). She said she had had it listed before but the listing expired & no one had bought it, so she was planning on relisting it. Long story short, I worked out a great deal with her for both games and it turns out that while the second one's CE box was open the game itself is still factory sealed. So I'd say from my experience there are more good, honest sellers than frauds on ebay, you just have to be careful & protect yourself.