I am currently trying to scratch a living as a gigging musician and this is exactly what happened in my industry.A few years ago,it was the norm to be paid a few quid,not much but at least something for your troubles,now that has completely been destroyed by bands(mostly young and impressionable) who are quite happy not only to receive nothing BUT WILLING TO PAY THE CLUB FOR THE PRIVILEGE OF PLAYING! Now it is not a question of how much you will be paid,it's a question of how much you are prepared to pay the greasy club owner for the honour of selling his beer in his rat-pit of a club for him.If this had been nipped in the bud as soon as it started,we would be in a better position to exercise our right to earn a living.We needed a stronger union and people willing to not take gigs,just so that they could get some exposure.Let those who bring in the revenue share in it also.Our particular case has gone too far down the drain to salvage,as the club owners have no shame in charging people to work and there are too many "scab" groups who would quite happily pay(usually very bad ones).
It must not become the norm for instructors to work for free as the next INEVITABLE step is instructors being charged for the privilege,and this would be an outright disgrace.
I gave up music to go into aviation and would hate to see the same thing happen here also.It has to become socially unnaceptable for instructors to work for free and undermine those who have chosen to make it a career.
At least in aviation you are not likely to be beaten to death with a base-ball bat for fighting for your rights.
El Cid