|Please note that this glitch only exists in the Japanese versions of the game, or is otherwise a glitch from a Pokémon game which was only released in Japan.
The Magikarp salesman glitch is a natural glitch only in Pokémon Red, Green, and Pokémon Blue (Japanese).
If the player tries to buy the Magikarp from the Magikarp salesman in the Route 3 Pokémon Center when they have a full party and a full current box, he will take 500 Pokédollars off them as they get a full box message, and they will not get the Magikarp. This can be repeated. This type of glitch does not occur with Game Corner prizes.
This glitch was fixed in Pokémon Yellow (Japanese) and the localizations, which do not take money off the player when they receive the full box message.