If something can be designed, then it can be altered too. Every machine in a casino has to be manufactured somewhere, and so simply interfering with the mechanisms before they leave the factory floor is the most effective way of cheating.
Security at online casinos is tight, and games are audited before they hit the virtual casino ‘floors’. Any irregularities with RTPs or jackpots are quickly spotted and rectified.
In the live arena, however, it’s far easier to tamper.
History is littered with cases of cheats using coat hangers to interfere with machines’ inner mechanisms, or ‘monkey paws’ which were inserted into machines to trigger the coin counter mechanism and make the machine dish out more money than it should have done.
‘Shaved coins’, meanwhile, are regular coins with a slight edge taken off. The slot machine’s optic sensor was tricked into thinking it was a regular coin but it would spit it out as a duff one once it passed through the machine. Therefore, cheats could continue playing a slot with a series of fake coins until the big jackpots hit.