I mostly rely on gut instinct. However, I do ask at a minimum for a name, email address and phone number, all of which will be checked through Client Eye. I also exchange quite a few emails/messages as I have found that men often show you who they are quite quickly. If it’s an outcall to a hotel, I will want a copy of the reservation, and if it’s an outcall to a private residence, I will might for proof of address. I always ask for a deposit. Until I receive this, I do not take the booking seriously. Once the deposit is accepted, then we can properly discuss things.
Sometimes I might ask for more information, particularly if it turns out we have work or something else in common as I need to ensure it’s not someone i know - I was once contacted by someone I used to work for. I declined him, naturally.