The game is played in all major European cities typically in the areas with the highest tourist concentration (for example: Rambla in Barcelona, Gran Via in Madrid, Kurfürstendamm in Berlin, Bahnhofsviertel in Frankfurt am Main). The actors are usually from Eastern Europe. The game is classified as illegal gambling in most countries and the actors are able to remove all traces of the game in seconds when authorities approach.
The actor will always place the ball and move the shells in such a manner that it is obvious to all close observers where the ball is. He then touches all three shells, as if to move them to their proper places (sometimes while saying "is the ball here, here, or here?"). This is the crucial time when the ball gets its final position: the first shell he touches is always the one that everybody knows the ball to be under; he takes the ball invisibly in his hand and moves it under the shell he touches next. This is sometimes facilitated by the fact that the ball is soft and can slide in and out of the hand while compressed. It's like religion: you can only see it if you know it already.
Then he asks the present tourists if they want to play. If one bites, they have to hand over the money and then they can lift a shell, invariably the wrong "obvious" one, and lose the money. Most people get angry about their stupidity at this point and play again, sometimes losing up to five times in a row.
If no tourist wants to play, one of the helpers plays in order to animate the tourists. The helper will either lift a shell which is "obviously" wrong and will lose his money, or he lifts the "obvious" shell and wins. He wins because the actor touched all three shells again, moving the ball back to the "obvious" shell.
I have seen one variant of this scheme: sometimes the actor will not move the ball away from its "obvious" position by touching the three shells until a tourist has handed him the money.
Occasionally, the first game will be played fairly for a lower amount, to entice the tourist to risk more money. Cheating will start with the following games. Sometimes repeat losers are kept in the gamee with an ocasional win.
Sometimes a helper of the actor will place a finger on the "obvious" shell, as if to help the playing tourist and prevent any irregularities. However, the actor will still touch the three shells, the helper lifts the finger shortly at exactly the right time and the ball again wanders to another shell invisibly. Or, as explained above, the adjustment takes place after the money has been handed over.