It's a generalisation I know, but in my experience as a customer, it was the weekend/part time/specialist/only do it for fun guys who did it best, because they were motivated by the job. UNfortunately you can only live on Tesco Value Baked Beans for so long, and they generally end up getting a job that pays proper money.
Of course if you added 10% to the cost of a lesson (which the average ppl student could easily afford) you could double the instructors salary and keep the good guys, which would be better for everyone surely?