This is a general rule in life and not specific to sp's or any specific job or area of life.
Dont fall in love with your lawyer, with your cashier, with your accountant, with your vet..
Why not?
What should be said is don't fall in love with anyone if it is not reciprocated.
i have never heard of a sp manipulating a client to fall in love for monetary gain, but i have heard that many times for strippers.
For sp's its the opposite actually, i know many people who have dated sp's, became good friends or having become casually dating.
OF course yes, you cannot let the fact that you are intimate cause you to develop emotions beyond that intimacy unless its mutual, but today the same can be said for any girl regardless of where you meet them because the majority of intimate relations always happen faster than any emotions can be developed, so this is by no means exclusive to sp's.
Imo the type of guy that would fall head over heels for a sp in a situation where its one sided and he is juste hopelessly in love, that type of person will fall in love with anyone in his life regardless of where it is, and develop that one sided attachement