@Kate31
Keep it simple and easy. For ex. "I see you're new on Airbnb and may not be familiar with how it works on trust and safety. I don't like taking in people of whom I don't know anything. Can you tell me a little bit about more yourself and why you are in the area?
If you don't have verified ID on, you could try turning it on. Every booking is normally set to any conditions prevalent at time of request, but since this is a security measure I'm speculating that it might perhaps override a previous choice of not requiring verified ID. Trying doesn't hurt. Airbnb seems to do a basic ID check, but the verified version is more work and might deter somebody who doesn't want everything on record.