You can ask for a written warranty or money back guarantee but, under the circumstances, the seller would probably say no (with good reason) and so would I if I was selling a car that didn't run.
You are buying a pig in a poke (google it if you don't know what that means), a car that is virtually junk.
Don't believe anything the seller tells you about the condition of the car (ran when parked, minor repairs, etc).
Assume that you will have to mechanically overhaul the whole car and offer a low enough price so that you can budget for extensive (and expensive) repairs.
That's what I do when I buy a project car.
To me, any car that has to be towed home is worth about $500.
If the seller won't sell it dirt cheap, walk away.
PS: You are to be commended for coming here with the question before buying the car.
Most people show up here after they've been burned and whine "What are my rights?"