I got a job at the front desk of a hotel, but the hotel hasn't opened yet. Is it reliable to go to work like this?

What you said is that the hotel is in the preparatory period. Generally, some hotels will conduct job recruitment during the preparation period, and train new employees during the preparation period, so that everyone can work normally when opening. But you can also observe it a few days before going to work. If you feel unreliable, you can leave your job quickly. After all, you can resign at any time during the probation period.