Many of the big players like HP and Dell have outlet sites where you can get scratch and dent or refurbished products for very similar prices. The only REAL value to ebay is if you can get an used part in a pure auction or if you need to find something out of production.
That being said, I buy refurb stuff all the time from ebay and have had no problems, but its usually the stuff that I can't find on the factory outlet sites, I always start with those before turning to ebay, because MOST fixed price sellers have their prices set at what new prices would be anyway so its hard to find REAL value on ebay... -_-
Dry