There are so many tools casinos can use to detect if a player is playing from a restricted region or not. Some of these tools are paid why some can be programmed. We don't have to think like we are smarter than the casino that allow us to play bet on their platform because they own our funds and can at the same time check if we are actually following their teams or not. There are plenty of ways to detect the . location of a player and when something is fishy, the casino can request for KYC from the player which is when everything will be unveiled.
I don't think casinos use third-party software to detect multiple accounts or players from restricted regions. Most casinos use their back panel to detect multiple accounts and find people from specified areas. Casinos have their own dedicated security department, and they have experienced people who can detect abusers. Otherwise, most casinos would have to stop their business because of the abusers.
Some people use Tor, VPN to change their IP address and location. In such cases, casinos ask them to complete KYC, where the abusers fail. Even if they submit fake documents, their documents gets rejected.