Betting is gambling, so there is always risk. These offers are labeled as risk free in that you get a refund in some form if your initial wager or wagers lose. It's simply designed to entice new customers. We recommend taking advantage of these one-time offers when registering at the top online betting sites.
Bet credits and bonus bets cannot be withdrawn, but they can be used to wager on other sporting markets your sportsbook has to offer. Some sportsbooks make you use your bonus funds or bet credits in one lump sum.