The jurisdiction is the State of Maryland in the USA, should that fact be of interest.
A friend of mine is involved in intractable dispute with the co-owner of a car. I'll call my friend Abe, and the other party Bella. All the agreements involved are handshake only. Abe inadvisedly co-signed a loan for Bella so she could buy an auto about 6 months ago. The deal was that Bella would make the payments on the car and would keep the car after the loan was paid off.
Of course the inevitable occurred and Bella stopped making payments. Bella also refuses to make the car available so it can be sold off to minimize Abe's losses. Thus the car will end up going into repossession and the cost of the repossession will be added to the loss column for Abe. Bella has terrible credit, so she has nothing to fear in that department. Bella is also a veteran thief and con artist with a long rap sheet and is currently on probation.
A further perplexing wrinkle that I don't really understand is that the MVA is refusing to issue title, tags, or registration. When I asked the MVA why they would only say there was an "insurance violation". Thus Bella is driving the car with long-expired temporary tags and probably no insurance. Both are listed on the title application, with Bella as the primary owner.
If Abe sued Bella to force Bella to do something sensible, like either make payments or surrender the car, what reasoning would the court use to evaluate the competing claims? Abe will say Bella was supposed to pay everything and Bella will say they were supposed to pay 50/50, or maybe even 5 Bella/95 Abe. If Bella could get away with it she'd say the car was a gift from Abe, but Bella also co-signed the loan so I doubt that would fly.
Bella will certainly ignore any judgement against her, but I don't that's relevant to the question. Also not relevant, Abe's current plan is to simply let the car get repossessed and eat the losses.