In the US regulated sports betting has grown significantly since the Professional and Amateur Sports Protection Act (PASPA) was overturned in 2018. This led to an increase in options for bettors to use regulated (legal) sportsbooks instead of unregulated (offshore) ones. Not all states/provinces have regulated sports betting, but the number is increasing.
Many matched bettors, especially those starting out, do not use unregulated sportsbooks. It is also always safest to use a regulated book.
Regulated sportsbooks, often called legal sportsbooks, are subject to regulations by the gaming commission for each state/province they operate in. This is important because the gaming commission for your state can help you in a situation where something goes wrong. If a sportsbook does not pay out a bet or if they don’t follow their promotion terms and conditions, you can go to the gaming commission for help. You will likely never have to contact the gaming commission, but the option is there should you need it. Each state/province has a gaming commission website that you can access and use to contact them if necessary.
Unregulated sportsbooks, often called offshore sportsbooks, can be considered a legal gray area. Most states/provinces do not have specific language that makes placing bets illegal, rather the action of taking bets is what's regulated. This allows nearly all Americans and Canadians to legally use unregulated sportsbooks with a few exceptions. The risk you take is that offshore sportsbooks are not subject to any local laws. So if you have any problems with them, such as not completing a withdrawal or having a bet graded incorrectly, you are at the mercy of their customer service with no third-party/government to help. Many unregulated books have been around for decades with strong customer service records, but the risk is still there.