Vi,
I'm glad you are now aware. If you are in vehicle that is driven by a taxi driver or former taxi driver, proof of relationship is a real thing and something nearly impossible to prove. As Accompong stated, insurance companies have lawyers sitting around finding any loophole they can to deny coverage. And something not mentioned, should you be in an accident and something or someone else is injured by an illegal taxi, you can also be held responsible for the damages. That has always been the case, the new law will only strengthen that issue.
Your friend knows the laws, for taxi or former taxi drivers, this is Driving 101. You can never become a taxi driver and not know this. Your friend's insurance policy is in the car. Read it. For private driver's its a one page document that specifically states that there is no coverage if the vehicle has paying passengers (livery) or the vehicle is being rented out. Those policies cost a lot more.
For regular, non taxi operating private drivers, this is not an issue. If a hotel manager, bank rep or shop owner stops to offer you a ride in the rain, A FREE RIDE, then all coverage applies. The local police know who is who and know to the best of their ability when a visitor is being helped for free by a private driver. I give my local neighbors a ride and even visitors from time to time, but I have never once charged anyone a taxi fee. The local police know this.
But with your friend's recent decision to give up the red plate, they will be targeted. Just ask my friend who got busted for actually offering a free ride. His position was indefensible even though he seriously wasn't charging. He is known as a taxi operator.
What proof could you give the officer that you didn't pay and never paid for your friend's services?
That is the question you have to ask yourself...