I imagine that most ladies in the business would find such a policy rather... 'Impractical', to put it politely...
Ask any lady in the business how many of their clients don't cum during their appointments, and you might be surprised when you hear the answer. There's no way that the ladies would be handing back a significant portion of their incomes because the guy came to visit the lady when he was unable to perform or reach orgasm.
Besides, you pay for 'time and companionship only'; there's no guarantee that you get to cum!
Fighting the Good Fight...