They are legit but they're also costly. You buy a bid package for say $50. Each bid costs you $.50. So you bid 10 times and may not get the article you were bidding on. Therefor you LOST the $50 and get nothing for it. You may get lucky and win something on just one or two bids but most times it's just not worth it.
My dh insisted it was a great way to get stuff until it cost him $40 for a $25 gift card!