I have been bidding and buying from QXL for a couple of years. Things I have bought have been three computers (one new, two refurbished Packard Bells in excellent condition). The Packard Bells came with a year warranty and when one of them had a problem a technician came and fixed it the next day. I have also bought televisions, a video recorder, various bits of computer hardware and a mobile phone, all at excellent prices.
When buying from QXL direct or one of their affiliate partners, once you have bid and won an auction you don't have to do another thing. Payment works by direct debit and you don't have to do another thing until you sign for delivery. All have always arrived in excellent condition. I hardly ever go any buy things from shops any more as I can nearly always find what I want through QXL at a much cheaper price.
A guide to successful bidding would be to thoroughly research prices (over the internet is best), decide on maximum price and go to the auction site a while before bidding closes so you can put your bid in just before it closes.