Trial shifts are a thing, but at least in the US they have to be paid to be legal. And wage theft, if reported, actually results in penalties for the fraudulent employer.
I’m guessing a lot of the teenagers that apply to work at restaurants that do these illegal, unpaid “trial shifts” aren’t aware of how illegal that is so they probably get away with it for far longer than they should.
Shit, a lot of adults in the US don’t know their federal and state rights as employees thanks to lack of education on labor laws. Laws only work if everyone is aware of them. Can’t report something if you don’t know it’s wrong in the first place.