Penny-auction sites are nothing new, and they are legit-ish.... Most of the legit ones do exactly as others have described; they auction off a high-dollar good (eg a 50" Smart TV) and the bids only go up a penny at a time. Since the bids go up only a penny at a time, the final price for the good ends up being very low (often 50% off or more). However the site makes money by making people purchase bids at a much higher price than the bid is actually worth. If you time the auction correctly and save your bids, you could actually do well with these penny auctions. Even if it actually costs $0.60 cents per bid, you might be able to win that smart TV by making only 50 bids or $30 worth of bids. However that really relies on how well a person times the auction. And that is made more difficult since most of these penny auctions will also increase the lot's auction time by usually a few seconds with each bid made. That means that even if you see a TV auction ending soon, you may still get into a bidding war with others and the time will keep extending out to allow others to jump in at the "last" second. For the legit sites, it could really be a win-win scenario where the winning bid has to only pay $50 for the smart TV (and when adding in the $30 spent on bids, gets the TV for only $80 total) and the site itself makes 5000 bids at $0.60 per bid = $3K for a $500 TV (and gets to advertise a 90% savings).
However, there are also some penny-auction sites that are even less legit than that. Some of those sites will actually have employees create accounts and create those bidding wars in order to rack up more profits for the site. Additionally, if those employee-accounts do end up being the highest bidder, the good will usually get recycled by the site for another auction. Thus a smart TV could end up being auctioned off several times before an actual customer wins it.