My friend doesn't have enough money to pay the hotel bill. Does this hotel have the right to detain my friend?

Hotels have no right to detain people. They will detain your friend. If your friends leave by force, they will "detain" them, or they will call the police and the police will adjust them. If the nature is bad, the police have the right to detain them.

If the money is similar, people will give you a discount or something. Forget it. If the difference is much worse, people are in business, and the cashier has no right to give you a waiver. If it is too much, the boss will quit. If you were the boss, you wouldn't do that, would you?