Only in dreams!
If it does happen, it happens as something any two consenting adults would do because of mutual attraction, chemistry, etc., not as a business proposition: an affair between professionals and their customers/clients is not something so unusual. Clients have been known to fuck their lawyers! *LOL*
But this is something that has been asked many times: what is the fascination? I very well understand the desire for a great massage combined with a happy ending: why does it have to be an RMT? It is reasonably available elsewhere!
Perry