MY chain rattle comes back when my oil is about 1/2 way down the dipstick between min and max, top it up again to max and it disappears. However these cars burn a fair amount of oil, so you end up doing it fortnightly or more depending how you drive it.
Using thicker oil is best too, when I was on Castrol Edge 5w30 it rattled a lot more than the 5w40 TPS (Quantum Platinum or something I think) oil I am using now, this also reduced the amount of oil it burns.
Ask for the car to be cold when you view it, start it up with the door / window open so you can listen for hte rattle, IMO if its 3 seconds or under then its fine and you can cure it with thicker oil and keeping it at max, if its much more than that the tensioner or guides are faulty, or the oil in the car is very thin, very old, or very low.
The rattle is a bit scary but its very rare that the engines fail because of this.
I would recommend listening for clunks and clicks whilst steering at low speeds, a set of front arms isn't cheap and it can involve a lot of labor changing them ,if it clicks / knocks you might be able to knock that expense off the cars sale price.
I ended up changing all the arms on mine. But it has done a few more miles than this one.
Good luck.