It's a co-buying website
The
FAQ will explain it better than me, but basically because they're purchasing products in bulk, the price that they pay is (usually) a lot less than retail. When the co-buy goes live, there's a limited number of items, and usually 99 hours for you to register your interest in a product, unless they all sell out before then. The more people that register interest in the product, the lower the price goes, but there's always a ''best price.''
E.g
http://www.buyapowa.com/deal/659, 17 people have signed up so far, and there are 30 units for sale for this co-buy in total. The best price is £34, and you'll pay this if 75% of the products get sold. The current price has moved down from RRP (£49) to £35 because people have signed up.
Scroll through
here and you'll see all the things that people have requested co-buys on. If you add your email address they'll send you updates to tell you when they go live.
It sounds complicated but it's really not. I've only used them this once, but people everywhere are raving about how good it is. I saved £30 on my Clarisonic, and they take payment through PayPal too (which made me feel way better about the whole thing, although I'm sure it is legit!)