I've bought all sorts of stuff off eBay, and been happy with the bargains I've got. But you absolutely need to know the value of what you're bidding on, and not get silly.
I've also seen things go for more than the new price (and reserve prices set at or above the new price) - particularly for computer equipment where the price has fallen recently.
I got an Airlite headset last week for £10 (not bad).
Last week I was bidding on a 2 inch dia 38mm f/l eyepiece for my telescope - second hand "going price" is about £50. It was a ten day auction; half an hour before it ended, my £37 bid was winning. In the last three minutes, three snipers bumped it up to £64. Daft.
I wondered if one was the seller trying to up his margin! My max bid was what I was prepared to pay for it (and no more).