I have frequently had to ask potential guests to add a photo of themselves - I usually say "... you can see my photo and my house, and I'd like to know I'm welcoming the correct person into my home where I live..."
I once had a photo of a duck try to book... so I said that I didn't have a pond so my place might not be a good fit. She changed her photo within a few minutes and was a great guest.
Newbies just don't understand the trust issue, especially when it's a room in a private house where the host lives full time.
I also ask them to write 3 sentences about themselves in their profile page... "Could you please finish your profile page...."