Probably not so much a ploy on the part of the organisation but perhaps on the part of the individual - you can qualify as a "PT" in about 6 weekend sessions here in the UK. But from what I can tell it's part "how to sucker people in and give them just enough results to keep them coming back" and "how not to kill people making them exercise" rather than "This is how you coach a squat" (and I say that because some of the squat form I see people exhibiting while under the instruction of PTs in my gym is fucking horrific) But yes, when the gym I go to did have that 1 fat PT they got all the fat guys and girls hiring them.