Bitcoin is a field to scammer because it is decentralized. And the fact that it is not yet moderated by the government so if you lost your coin. It is hard to get it back or even trace the scammer. We do not have that security in bitcoin as in fiat. But, the risk is still in us. If we follow the proper process of sending money to others, we can lessen the risk of loosing it if we make it in public or hire an escrow etc...
It is not particularly different with centralized currencies either
I guess centralized or decentralized nature of a currency doesn't have much to do with that. There were plenty of scamming enterprises long before (actually centuries before) the birth of Bitcoin. If you look through history you will find scams and pyramid schemes dated as back as early 18th century. I refer here to, for example, the history of the South Sea Company. It seems that you most likely talk about the irreversibility of Bitcoin payments but this is only a minor issue (in respect to frauds and similar scheme). There are quite a few of Ponzi scheme companies active today which are involved with fiat mostly