In a sufficiently large population, over a finite period of time, there can be a small set of people that look like they are winners. This is called survivorship bias. Given enough time, these people will eventually lose.
However, anyone saying they know how to win on slot machines is probably just lying.
The house always wins in the end. The only way to win as a player is to cheat.
Some days he would work all day and see people put money in a machine and not win anything much (e.g. jackpot never came up). Believing that the machine had a payback rate that would balance out over a few hours/days, he would deliberately put a bit of money in at the end of the 'no winner days', and would often win enough that it made it worthwhile overall.
Anecdotal, but it seems consistent with your understanding and is a source of an edge.
Each spin has an equal chance of winning. The payback is adjustable in the software, but it does not pay extra when it's behind.
Of course, sometimes the jackpot is larger and that's a better time to play (but still not a good time).
However, I do not know what the situation is in the UK/EU at present, and I do not know what it was 20 years ago (when my brother was working there).
Doesn't mean the house would lose.
The advantage players would fight for the machine(s, if a pooled jackpot) and play until the jackpot was hit, at which point it would become -EV again and they would stop.
These machines are relatively uncommon, and getting more uncommon.
You can read about these players, I think they can squeak by making about minimum wage or thereabouts.
You are absolutely wrong, but your comment did manage to get mine to -1 point, so thanks for that. You are correct that slots are as random as the RNG within them (which, as it turns out, isn't actually that random [2]), however that does not mean they cannot be beaten. Slots can be beaten in a variety of ways:
1) Any progressive jackpot that gets high enough can skew the game's return to players to above 100%. Believe it or not, digital slot reels can be mapped out and the return extrapolated (example here [1]). On a progressive slot, with this data and the meter rise in hand (which can usually be easily calculated through mere observation), you can calculate the level at which the progressive makes the game positive.
2) Various slot promotions can be beaten. For example, there was a casino team that was tipped off to a promotion where a casino in the midwest was, for 12 hours, offering a double payout any W-2G win (any win over $1200 on a machine). So, they went and played a $100 slot machine, where almost any payout was over $1200 - essentially getting a double payout on every win. They had an enormous advantage with this promotion. These kinds of mathematically challenged promotions are not as rare as you would think.
3) Many slot machines have a "must hit by" feature, where the progressive must hit when it reaches a certain amount. Advantage players wait for these to get to within cents of the payout, locking up machines hours before and playing the minimum amount very slowly, so that they are in a position to win them.
4) Some casinos give loss rebates to some players that can turn almost any game positive, especially when combined with techniques that I won't mention here. This isn't necessarily limited to ultra high-rollers either - I am familiar with a few casinos where significant loss rebates start at losses of just $1,000.
There are more.
So you are absolutely wrong that there are not advantage slot players. There are teams of them that work in Vegas and other jurisdictions.
[1] https://wizardofodds.com/games/slots/hot-roll/
[2] https://www.wired.com/2017/02/russians-engineer-brilliant-sl...