I spent a year building slot machines for one of the biggest manufacturers. When a machine is built the very first thing that happens is a build sheet with the serial number plate and the odds sheet. They know what the payout will be before any part of the machine is even built.

Now the thing to know is that not all machines have the same payout. If there are 30 machines in an order most will have very bad payout odds of like 88% (sometimes worse). That means that over 1 million plays the machines will payout 88 cents for every dollar payed. There is literally no way that changes. It is hard coded in a chip on the machine motherboard. So every time somebody does win the odds are literally even worse for the remaining players. They will make 2 or 3 machines with better payout of like 97%. They will then use that to advertise that they have slots "up to" 97%. But unless you saw the odds sheet you would have no way to know which machine is which on the casino floor.

Casinos are for losers. There are only a few games where skill has any part in things and even then you have to be VERY good for it to matter. Otherwise you are paying for entertainment. That is fine but people need to know that and budget accordingly.