I look for prospective guests who have offline verification, a clear photo, and send a polite message explaining why they are visiting and the composition of their party.
If they have done all that I consider that they are reasonable people who are used to play by the rules, as Airbnb displays a message inviting you to do so when you’re about to send an enquiry. If their message do not follow the rules, I ask them to do so, and most of the time I never hear back from them. Problem solved.
I think that I also indirectly filter guests because my listing is more expensive than comparable listings in my area (size and occupancy) so I guess that people send an enquiry cause they really like my listing, not because I am one of the cheapest options.
I rent a separate unit though, if it was a room in my home I would engage in a conversation to really screen guests.