Welcome to BHQ. Lack of maintenance, care, knowledge, proper oil/ fuel are about the only thing that will cause it to blow. Things do wear out, how you treat it determins how quickly. I'm sure others will give simular response. As far as the purchase does he have reciepts for parts/work? Set front up on crate and check all suspension, do same with rear. Get a compression gauge and check motor. That fresh with milled head should read 135 minimum. When you pull plug it shoul be tan colored. If he won't let you do comp test beware. Be sure to ask what fuel/oil he uses.
Good luck and let us know.
JMHO, your results may , and will, vary