Under oath!
According to Torah Law, people are ordered to take an oath (shevua) when they deny money that is claimed from them.
Sometimes, however, the rules of the game change, and the plaintiff is the one that takes the shevua (and subsequently the claimed money).
Such is the case of workers who claimed that they weren’t paid by their employer (while s/he said s/he did). Why is that the exception to the rule? Watch this video and get the picture.