Do you have any reviews? Perhaps they are competition in your area trying to do market research or they don’t know how Airbnb works. I would not give them tours, this is not like renting a space where you tour it before you decide to apply. They should book based on your write up, pictures, answering any questions they have, your reviews and the feel they get off your listing. And giving tours is time consuming. How many of those tours ended up in successful bookings and stays?
One more thing, they could be scoping your house out for something. Some people could use this as an excuse to get a layout of the house and see if there’s anything valuable present.