I was for a while an avid ebay user, then there was a dispute about a 15p charge, for which they slapped on £5 default payment which I refused to pay, so they banned me. That was about 5 years ago, and to be honest I haven't missed it, and with the horror stories I hear about rogue traders, I'm glad I don't bother with it.
I prefer to trade with a few tried and tested companies, or go to ones that have been recommended personally. I tend to mostly use ebuyer, play.com, hmv.co.uk. On a side note, one thing I found out with Currys, is if you order something online to pick up in-store you sometimes get the item cheaper than the in-store price... well worth remembering.