@Brian-And-Laurie0 If your guest is having difficulty booking, I would get them to contact Airbnb. If there is a problem with a site, you can't do anything to fix it, nor can you initiate a booking on his behalf, so it's best just to direct him to customer service.
I've never seen a listing before where you can't contact the host before booking. The box is down at the bottom of the listing, though, completely seperate from the booking button at the top. My guess would be that they're only looking at the top of the listing. Have them scroll down and look for the Contact Host button, which is with your host information. He can enter the dates and send an inquiry, and you can generate a special offer from that inquiry.