You should develop a personal, ideally multi-level customer selection to check that you are dealing with a reputable customer.
You have to learn to distinguish good and reputable customers from untrustworthy customers. The gut feeling alone is not enough, but it is a basis. The selection includes the assessment of the customer, his intentions, his character: personal address, tone, content of the mail and personal phone call. A preliminary discussion is always useful, especially for new customers. Personal and verifiable data such as name, telephone number and address should be conveyed to you promptly and easily, so that nothing stands in the way of a call back and review before you set off.
The mobile phone number is not sufficient to check the presence, whether when visiting the house or hotel, unless you calculate a fake risk. You should insist on landline numbers and when visiting a hotel for the extension to the room, room number and name, to compare the information and for a better feeling before a date. Unfortunately there are people who like escorts to go into the blue. Goodwill is not appropriate for customer screening, but rather a realistic assessment of the situation and the build-up of the necessary trust is required in a short time. You should not rely on good faith, especially with a customer who is still a stranger to you.
Exchange ideas with colleagues and ask them how they rate a reputable customer. Good negotiations about price and service, clear announcements and money in advance are the basics. Customers who want to negotiate prices are a plague. Don't let yourself get involved.
There is a lot of experience in this job. Thanks to the dissemination of information and advice, you shouldn't get involved in the trial and error method. That would be naive. Being professional in this job means being careful and exercising caution. For your own protection.