If the owner doesn’t have their commercial certificate then you cannot charge people for your services as a pilot. You can share the operating costs though. Not sure about the legalities involved if they do hold their commercial though.

no man why fly when you can drive

If you “advertise” cost sharing then the IRS probably wouldn’t look at it as sharing. I would be very careful, the FAA and the IRS are looking into this more and more each day. And if you have an accident there is no way to “defer” liability to the operator. You most certainly would have some sort of liability, no matter if you shared, rented, gave it away, or pretty much anything else.

You want to have your cake and eat it too?

You can not charge a “guest” as a jet share holder/card member because you are not the certificate holder. You can share expenses with a guest if you are a private jet owner.
Only Part 121(Air Carriers & Operators) certificate holders can advertise “scheduled flights”. Private jets are flown under Part 91(General Flight Rules) and Charter jets are flown under Part 135 (Commuter & On-Demand operations).

If you’re a jet share holder and you charge one of your guests for a flight than you could be sued by just about everybody involved. Now lets say, if you take a “friend” to Las Vegas and back on your jet and later that “friend” where to give you a new Mercedes for your birthdate, than that would be perfectly legal.