The previous person has given the best advice. I am an avid ebay'r. As with anything, do your research before you purchase anything. If you do your reseach and only buy from people with a good rating, I doubt you'll have any problems. I purchased nearly everything off ebay, most of it I purchased from other people, but new items. I must say as a newbie R/C'r...be sure to do plenty of research..
The only "bad" purchase I have made was actually from here. I purchased some servo's for $30 from someone here and it turns out they were in a semi-serious crash. I deduced this by the hard scrapes in the side of two of them, and the screw that is only half-screwed in on one of the others. When purchasing servo's or the receiver, be sure to ask if it has been in a crash if buying used!!!
I've decided the best thing to do is to purchase some new standard servo's, that way I can be sure to minimize the failure risk as much as possible. I will be purchasing those off ebay too