Is it illegal to resell hotel rooms to earn the difference?

It is illegal to act, but if an agreement has been reached with the employer, the employer needs to pay you salary and commission.

Legal basis: Article 30 of the Labor Contract Law of People's Republic of China (PRC) * * * The employing unit shall pay the laborer's labor remuneration in full and on time in accordance with the stipulations of the labor contract and the provisions of the state. If the employer is in arrears or fails to pay the labor remuneration in full, the employee may apply to the local people's court for a payment order according to law, and the people's court shall issue a payment order according to law.