It is not a sale until there is an exchange of money. A client, by definition, is someone who pays for your services. Therefore, if you do not have clients make arrangements to pay at the time they make the appointment, and they don't show, the time is gone. You don't get paid and you have no client. Sitting around waiting for a no-show who didn’t call…remember what it feels like to be a piece of used toilet paper?
It is impossible to foreclose on services. If you can afford to live without the income, you can take chances. I have a choice these days. I can accept the word of a client that they will make regular payments after the fact, or I can spend time playing with my granddaughter. I don’t like chasing down bad debts, so I insist on full payment up front. If the person resists, she is not a client and I can choose to play with my granddaughter instead. My choice.