You can trust the casino license.
The casino does not need to cheat on slot games. If the gambler loses too quickly without ever winning, he will not play the slot again.

If you don't have a huge balance, you don't have to worry about cheating.
At some point, you may not trust casinos. Some had acquired a license just to look like it was legit but behind this paper and certification, illegal activities have been their doings. We can compare to casinos if we keep losing to one of them, while the other we can win - that is something questionable and for sure there is a sort of manipulation on the machines. It gonna be cheating. It was better to gamble where know that we are not cheated, at least if we lose, we know that we are unlucky that day, not because someone cheated us.