Eventually, the casinos wised up and changed it so the wagering had to be done on slots, which have terrible odds. However, we figured out early on (I was in an advantage gambler forum) that there were "double or nothing" games in the slot machine, that let you go double-or-nothing between 5 and 10 times. These counted towards wagering, and were essentially perfect 50/50 odds (no house edge) - so by always going double or nothing until the end, you could rack up most of your wagers at 50/50 even though the initial slot roll was at a much higher house edge.
I think I started with $100 deposit into a casino and probably made > $50k in the two years after that. About $40k of that went to bills and $10k became my initial poker bankroll while I taught myself to play poker professionally, which I did for the rest of grad school after the casino bonus gambling winded down (they eventually wised up to the slot machine thing too) -- and if you player poker at a high enough level and you use judicious table selection, you can always advantage gamble (because you are gambling with each other, not the house, though the house gets their cut with the rake -- so you have to win at a high enough level that you know you are beating the rake)
I was a "small time" person, just doing it on the side to earn spending money -- there were certainly other people who had many many computers, VPNs, shill addresses, etc who took those casinos for hundreds of thousands a year for those couple years.
I learned a lot about probability theory, estimated value, and the mathematics of gambling in general, gained the emotional strength to deal with high variance (the best description of playing poker professionally that I ever heard was that it was like playing a game of chess for $1, then flipping a coin for $100. In the long run that chess game is the only thing that matters, but in the short run those coin flips can be brutal). Good times.