If there is an incident the bottom feeding lawyers get everyone in their sights and get eventually find out everyone's certification level. Try to hide the face you are a "dive pro" and it will be discovered.
Dive pros carry liability insurance and there for the insurance company has deep pockets.
I was on a charter where a fatality occurred. Even though I was a paying passenger, had no co,none it on to the diver that died, I was sued. Went no where , was found that I had no liability with the incident , my liability insurance worked and costs me nothing financially.
As to getting stuck with a newbie, simple solution, inform crew that you expect your charter to be no charge and that you charge $200. Per dive to accompany said newbie. Shuts them down real fast. If it does not then look at it this way , for a two tank dive you just made $400.
to swim around a bit in circles.