Legal Question in Real Estate Law in California

There is nothing you can do to 'protect' yourself if you let someone take your car. You remain liable for the payments and 'turn in' of the undamaged car at the end of lease, no matter what he does. You probably are breaching your lease terms as well.

Not recommended. Your lease probably forbids any "commercial use" of the car, and certainly using it to go into the subleasing business is going to fall into that category, even if they have somehow forgotten to forbid subleasing specifically. If the man can afford to pay you a price that would compensate you for the big risks you'd be taking, he can also afford to rent or lease from someone already in the business.