@Marcel2361
Talk. See what they have to say. Tell them you want your guests to be happy with their booking so please could you tell me about yourself and those staying, and the nature of your visit? The answers can be revealing. Or comforting. It's really up to you! (In fact, prevention is solely your problem 🤨).
Avoid declining. It has some minor penalties, and if you decline often, the penalties can become major, so you should play the decline card very sparingly. If you find the guest to be risky or are very uncomfortable, scare them away somehow (encourage >them< to withdraw) . Demanding a big security deposit usually does the trick.
Welcome to hosting. Most of the time, it's really rewarding. But when it's not, it can be very, very stressful. Watch your back!