That's clean as fuck, but it's probably best to stay away from the older yz 125's like that, you can only get bottom end parts from the dealership and they're crazy expensive, and yz125's eat bottom ends so you would probably end up needing one in no time.
I'd ask him if he knows how many hours are on the bottom end/crankshaft, if it's under 50 hours you should be fine but if it's closer to 120-200 hours it's a ticking time bomb, that's how the guy who owned my yz killed it.