I agree with nottrusting that probably, as in all domains, there are Ts who might behave unethically or work only for money... But I don't think that it is very common, it would be pretty painful for a T to spend many hours per day with clients who they wouldn't like and didn't care about... I at least do care about my students and co-workers even if I think that I wouldn't like to work for free
And I am quite lucky as I'm pretty sure that my T doesn't do it, she's totally booked and she could always find clients so she doesn't have to keep someone only to get more money. I wouldn't ask her to work with me for free though. Like I wouldn't ask my sister to do something big and related to her occupation for free to me, I like her and I respect her job and I would be even more than happy to pay for it as that's what she does for living... And while I think that probably my sister would insist to do something like that for free, I would never expect someone else to do it...