I don't like to buy used gear. I'm not making any comments on any particular seller, just in general.
There are too many knuckleheads out there that don't even know how to correctly match equipment together in the first place, then don't know how to set it up, then overdrive the shit out of it. Then when finnaly realize it sounds like ***, not realizing they are the problem, they sell it to you. This is especially true of low end gear, from noobs.
Then there are the experienced (unscrupoulous) bass heads that buy good stuff, pound the hell out of it till they know it's near death, then sell it off to noobs who only know the brand name. Especially true of certain "competition" guys who sell of thier abused batteries, amps and subs as "almost new".
Between those guys and all the really bad online dealers selling refurbished, repaired and counterfit gear as new gear, I usually prefer to pay a little more and buy new from authorized dealers when ever possible. Other than authorized dealers, the best way is from well known members with good rep on forums like this. I've never done it, but I probably will someday.
Ebay sucks balls.