No bookmaker wants to experience losses by finding its gamblers winning too often. They will try to prevent these gamblers from winning more often, especially those who still win big often. If they only win with small wins, the bookmaker still allows them to keep betting. There are profitable players in sports betting. It's just that we don't know for sure because they also don't say that they are the lucky players. This is normal because they can keep betting on sports betting without anyone knowing about their winnings. Apart from that, they can also hide their identity from other people because if someone finds out, they will ask that person for tips.
Usually bookies will fool gamblers by giving unreasonable odds and this is very effective in making gamblers make mistakes when choosing the team or player to bet on.
So far there are no various ways that gamblers can actually make bookies suffer massive losses unless there is luck factor that is on the gamblers side, there are also some things that are quite annoying, namely placing limits on gamblers who often win the bet.
Isn't this very unfortunate thing because bookmakers always use various methods to prevent gamblers from winning, but even so, I still believe that big bookmakers will never disappoint gamblers, especially loyal customers.
But you are right that no one will admit that they have carried out various betting activities that are often carried out, what more, for win they will always hide every win they get, apart from avoiding requests for tips and also to avoid bad things such as blackmail or robbery.
Moreover, there are many smart people like hackers who can break into the private wallets that we use.