@Toby56 I also only host single travelers in my one guest room with ensuite bath. I do say "For Solo Travelers" as part of my listing heading. Most guests have found that clear, but I still get the occasional Inquiry asking "So is it just for one person?". Duh. These are all from quite young looking people, and new to Airbnb. I've never used IB, so it's easier for me to head off inappropriate Inquiries or Requests before the guest books.
But I also re-iterate the solo guest only in a message when I get a Request to Book. "Just want to make sure you thoroughly read the listing decsription and understand that the room is for 1 guest only."
I did have one young woman book for 1, show up alone, then emerge from her room the next morning with a guy. Turned out he was her boyfriend who had been away working out of the country- they had a plan to meet up here, but he was hitchhiking and she didn't know when he'd turn up. When I told her she booked for one and I only host 1 guest at a time, she looked so shocked and crestfallen that it was obvious she was really unaware that this wouldn't be okay (she also introduced him quite openly to me right away, it wasn't like she was trying to sneak him in or out)- she was new to Airbnb and figured if she was willing to share the single bed, it would be fine.
As they were both very sweet and obviously weren't trying to pull a scam, I just let him stay, charged them a bit more, and let it go.
Hasn't happened again, but as I say, I now message guests for confirmation that they understand the "Solo guest".