It may be a perfectly genuine request, some people can be very picky, and if he's in the area already then he maybe doesn't see anything unusual about asking to be able to view your property first. But Airbnb doesn't allow you to exchange private contact details (phone numbers, email addresses etc) with guests at the enquiry or booking request stages, so you won't be able to provide the guest with your address until they have made a confirmed booking, which I guess would defeat the purpose of his request. Just explain this to him, and advise that your listing has images of your property which reflect a true and accurate likeness, and if he has a genuine interest in staying at your place, then he should be happy to book based on this.