Once the machines went electronic, I was done with them, given how easy it is for insiders to rig them. And yes, I’m aware, towards the end, even the ‘mechanical’ machines were chip-controlled regarding their outcomes.
The payout percentages can be set. Here in the States they are mostly set at about 93% and I believe that is by law. Other countries have different payout settings. In Colombia it is really LOUSY. I was at a casino (and they are really crappy, as in industrial park crappy) and the settings are about 60%. So basically you feed your money in the slots with NOTHING coming back except rarely. Its like they don't want to give you a bit of enticement. Plus the casino I was in had NO fun atmosphere at all. When I asked for some water, they gave me a glass and told me I could get it out of the sink in the bathroom.