Players "bid" for items using gold trophies. They didn't lose them, they just can't only be used to bid on other upcoming items.
The first item up for bidding was a costume from Killzone, which a user named REDSOXFAN95 won - and was immediately pegged as a cheater, since apparently REDSOXFAN95 had somehow won 8000 gold trophies in the space of roughly 6 weeks.
Sony has had an issue with hackers cheating with trophies and leaderboards in the, and it's likely REDSOXFAN95 used one of them to illegally gain trophies.
It'll be interesting to see how Sony deals with the other bidding items, since it's quite possible a user will cheat and not be so obvious about it as REDSOXFAN95 was.