no its not a scam, basically if i understand them right then the last bidder wins (as he/she will be the highest) but every bid increases the time the auction goes on for (there is a max length though) so even when its about to get to 0 seconds for you to win there will be loads of people waiting to bid and it will go back up to X mins again.
Don't use them, not unless you want to throw money away
How can you say its not a scam without having a scooby?
Every bid adds 15 seconds to the timer, so everyone is putting last minute bids in so normally PS3s sell for £50 ish. starting at £0.01 (each bid adds £0.07 to the bid price) which is over 700 bids. 700 bids x 50p + £50 for the console = £400 for a console that costs £270 max...