you have to be careful for sure. But good deals are to be had, off of ebay. It takes experience and patients. If your in a hurry to buy the first thing to come up for sale, its easier to get screwed.
I bought and built my whole quad off of ebay. sure I got screwed once or twice but the $$ ive saved off of everything else made up for the screwin I got.
It all comes down to being very carefull and selective from who you buy from