If you arrive at a parlour or brothel and the worker/s you were hoping to see are not what you were expecting, you are not obliged to pay for any service and you can leave and go somewhere else. Once your session is over you should not expect to get a refund if you were not 100% happy with the service.
With escort agencies if you are not satisfied with the person they have agreed to send out to you, you would normally have to pay a cancellation fee. This varies between agencies. You should ask at the time of the booking about their cancellation policy. For example, you may be asked to pay travel expenses.
With private sex workers it is up to the individual worker but generally you should expect to pay a cancellation fee or the worker’s travel costs if you decide not to stay or have them stay. This price will vary from worker to worker.