Deterrent needed?
Well, if it is deterrent you seek re' grey chartering perhaps this legal upgrade affecting Europe's coach and road haulage industries from February 2022 may bring hope:
" 7. Joint liability of shippers
A joint liability principle was introduced, whereby shippers can be held liable for the infringements committed by the hauliers they use where they knew or ought to have known the transport services they commissioned involved infringements. "
Were AOC law to include a similar principle it would become easier for CAA, etc, to go after all those in the background, at least in future cases. Perhaps more importantly the deterrent effect could well be significant, instantaneous and all at minimal cost.
Just a thought...