Properly well-regulated casinos should have a code of standards and must comply to serious regulatory and legislative requirements of state bodies. This prevents casinos from dishonest practices. Each Casino gets held to account by the legal body which oversees its functioning. State-specific, recognized licensing authorities license all of the casinos & slot sites listed at CasinoRange. So yes, a Casino can cheat on slot machines if they are not licensed - for the respectable options, it's really not in their best interests. Licensed venues are not able to alter anything on the slot games.