The hotel made a mistake when checking out and refunded the guest more money. Is the guest obliged to return it?

In a society ruled by law, any income should be legal. The General Principles of the Civil Law stipulates that an act that causes losses to others and gains improper benefits without legal basis belongs to unjust enrichment, and the person who gains benefits shall return the improper benefits to the person who has suffered losses. It can be seen that unjust enrichment should have four elements, namely: one party obtains benefits; Others suffer; There is a causal relationship between gaining benefits and suffering losses; There is no legal basis for obtaining benefits.

You can ask the customer for a refund.