My car has been decades in the making because I've been taken advantage of (a lot) and until recently I just didn't know any better. It's good of you to try to be upstanding, but the point of a non-refundable deposit is that if you decide to walk away, the seller get's your deposit for his time and trouble (and in this case, I think, more than enough). If I were in your position now, I'd turn my back on this purchase and keep looking.