In my experience, having bought two Whites detectors off eBay (a DFX and MXT), I'd say if you went thru eBay and bought from a person with good feedback you can get a really good detector. For example, I bought my DFX for $550 and used it for the entire 2009 season. I sent it into Whites near the end of the season to get the toggle switch replaced and also to voluntarily get a new LCD screeen put in because some pixels were fading (wasn't necessary but did it anyway). All these repairs costed a $167. White's Centreville shop was great with the service and turn around time. Decided over the winter to jump into a V3 and reluctantly sold the DFX on eBay to offset some of the cost of the new V3. I ended up getting $560 (minus $26 bucks in eBay fees and $18 shipping), so for a whole year I was out 200 bucks. However, I did find $135 in clad, nickles, and pennies of which included 40 silver coins, 1927 10KT gold class ring, 160 wheats , 22 IH's, other miscellaneous items and 100's of hours of FUN.
To summarize, I was very happy with the resale value of my Whites DFX detector and all the stuff it found!!!!!