So just as a hypothetical example, A charter brings a paying client to Teterboro NY. The return expenses were covered by agreed upon fee. That plane needs to reposition to Van Nuys CA and is empty. Would it be reasonable to offer pilot or owner $2-3k cash to ride back to Van Nuys with my wife and child? Or does liability make not worth while for operator?
Thanks for all the input in this thread btw
Absolutely positively no! That's the whole reason for operational control because that stuff was happening.
You'd have to book the flight through the operator and while cash is a viable means of payment, paying the pilots/owner directly would be an illegal charter.
And there's absolutely no reason to book an illegal charter if you're a charter certificate holder already...yet some do.

What could be done in that case if I were approached by a family member would be to add you to the manifest and your names get checked against the no fly list. If you were interested in paying then I'd put you in touch with the charter sales folks and you'd make whatever deal you wanted. I doubt they'd take the trip for just a few grand but anythings possible.
Me personally if we're paid to fly empty then I know the cabin isn't going to get screwed up on that leg and the flight attendant has plenty of time to get the airplane squared away so there's no extra work when we get back home.
I've flown my family before on empty legs. Each time was with the approval of the operator and adding them to the manifest just the way you would a regular charter customer. Except they didn't pay. There is a small per head tax that's less than 5 bucks but the company folds that into our monthly statement and the airplane owners never made us pay it back.