Then they just have a communication problem and clear that up. Come on, that's not rocket science.
So back to my example. The guy playing a monk thought he could do a Flash tornado. It did not fit the theme or style of the campaign in any way shape or form. This is not a communication problem, it's someone making up a powerful class feature that did not exist because I'm not running a superhero campaign.
How does it get resolved? Come on, this question is not rocket science.