Obviously something was wrong. He took it out and took it apart. Looks to be like it had a bad head gasket (rust between two cylinders And at the ridge of the right cylinder) and at least the head could be bad. Those heads are prone to cracking when over heated. All of this is guessing! You wont know till you get it cleaned up and checked. But $500.00 is not a good deal for YOU! I learned the hard way.