But if his story is true, he can probably show-

1. His flights are incidental to his business in that he goes only to place B or C and comes straight back to place A afterwards. Or, if elsewhere his various destinations are easily shown to be legitimate work places with documentation for everyone since he may be going to a job site instead of a formal location.
2. The flight times form a pattern supporting a work schedule which is easily verified.
3. The passengers are known coworkers and colleagues and a log of their contributions, flights etc. is kept.
4. The destination is not some resort location unless it can be shown the resort is a work place.
5. Holding out was minimal (technically none) and consisted of word of mouth among colleagues. Craigslist is not a good idea.

If these conditions all exist in essence, I do not see why he can't use the private pilot rule about sharing expenses (14 CFR FAR 61.113(b)(1)) to make these flights. The use of a turbine is little exotic, but there are private pilots who own and operate some smaller passenger turbines such as King Airs and Meridians. But the story needs to check out.