I'm a big fan of Ffordes. But aperture UK are worth a look too and if it's Nikon related, Grays, although don't expect any bargains!
It's also worth mentioning that sensible use of ebay can still turn up great gear. If a listing contains plenty of detailed information, good and bad, that clearly identifies that the seller knows what they're talking about and has good feedback to back it up, then combined with buyer protection via paypal, it is among the safer methods of buying.
There have always been untrustworthy sellers. There was a shop in Camden Town (London) that was infamous for its behaviour but people still kept buying from them. I've bought 2 items from Rocky. One was just fine and the other was rubbish. As both items together were less than £20 I thought it was a reasonable result given all the stories in circulation.
Yea, it took a crazy amount of emails and me saying I’d take him to Smalls claims before he refunded the camera. Don’t know if I actually would have for £70 but it worked. Took about a month.
I’ve bought a couple of things from ffordes, always been really good. I bought a mamiya 45mm lens for a 645 camera and a prism view finder for the same camera. The lens was perfect and they even went through their stock to pick the best viewfinder they had.