The one thing is that if there were any problems playing a disc/episode or two, a return wouldn't really be feasible (I think it's 7 days, so...). But I've never had problems buying stuff from them.
ETA: Hmm. You can get all 3 seasons new on Amazon.com ("An Amazon.com exclusive") for just $145, with free shipping and probably no tax depending on where you live. For only $30 more, new is probably a much better deal. Oh well. :)
ETA2: And on deepdiscountdvd.com, it looks as if all three season sets add up to $133.