Well, the problem there is you have to pay for each bid. Add to that, the fact that there are a lot of people who are one 24/7 bidding on stuff, what you get is an item where the auction never ends until the item is around the retail price or often higher, and then if you finally get it, it's way over priced because not only do you pay the retail price for it, you also paid for ever bid you placed.
My advice for you is: don't get scammed by any of those sites. If you want to go ahead and try it, I'm not saying you shouldn't, but just be careful because it's very easy to pay twice or thrice the retail price for an item and never even win it.