I don't see the issue. If you feel so elevated that you can speak disrepectfully of someone, then that's great. You are paying for the ability to do that. If you provide a sexual service and baulk at the idea of repeat business with a certain client, but either do it for the money or block them, then great, you have equality of bargaining power to do so. If a service provider starts to get all damp eyed over one of their clients, then great, that's quite nice. If a client really likes a service provider and repeatedly sees her, then great, that's equally as lovely.
If the feelings are reciprocated, then great, have a relationship, if they aren't, then great, don't have a relationship.
This whole make believe ethics committee on who should see whom, for what reason and when, this whole line-crossing nonsense, it's all a bit made up.
Some clients would never see a service provider, on the grounds that they are a service provider, that's fair enough but perhaps they would do well to remember that they are the ones that are paying for sex. Those service providers who scoff at their clients having to pay for sex would do well to remember that they are the ones selling it and are not in a position to start moralising.
If you start to fall for a service provider, then the onus is on you. If she starts to fall for you then the onus is on her. If you believe that she is falling for you then you are probably wrong, and if she believes you are falling for her she will milk it until you have no more money to spend.