This is not that serious of a post, but I feel like this could be a good way to make money. Maybe the people who scam foreigners in Europe can try this to see if it actually works well.

It would work by using the game of Nim. Basically, in the game of Nim, two players take turns removing a positive number of stones from exactly one of some number of piles of stones. The player who can't make a move loses. You can read about it here. Basically, if the $$$XOR$$$ of the number of stones in each pile is greater than $$$0$$$, the player who makes the first move, Alice, can always force a win. Otherwise, Bob can always force a win (because after Alice's turn, the game would transition to a state where the $$$XOR$$$ is greater than $$$0$$$).

So here's what you would do. First, set up a table near some popular site. When someone (Bob) comes your way, explain the rules of the game to them. Then gather $$$30-40$$$ matches and tell them to arrange the matches in $$$4-7$$$ piles however they want. Also, make a bet for some amount of money. Then you make the first move. If you know what you're doing, you will win in most cases, because the probability that the $$$XOR$$$ of the matches is greater than $$$0$$$ is very high. Furthermore, if you have an odd number of matches in total, the $$$XOR$$$ of the piles will always be greater than $$$0$$$, so you can never lose the game as long as you go first.

But this trick has more potential. If they get suspicious that you are making the first move, tell them that they can make the first move (or ask them if they want to flip a coin for the first move). The chance that the $$$XOR$$$ of the match piles is greater than $$$0$$$ after their turn is still very high. And even if it weren't, they would likely make a mistake somewhere along the way, unless they also know what they're doing.

If they lose and they want a rematch but they are suspicious of you, you can switch it around: now the player who makes the last move loses. Luckily, this variant (called a misère game) works almost exactly the same as a Nim game, so you still have a very high chance of winning.

Now if you're at your table alone, no one is really going to approach you. So you should hire a few people to come up and "play" a game with you every now and then so that you seem more approachable. Also, you should lose maybe half of the "games" you play with your employees so that the onlookers feel like they have a chance.

If you combine all of this with a personality that implies that you don't really know what you're doing, I think that you could really make a lot of money. Many people will think that they're smarter than you, but not many will be well-versed in the Sprague-Grundy theorem.