I looked at a '94 E320 Wagon today. The current owner is not a car guy and admitted to calling his mechanic at one point complaining about pinging noises from his engine when climbing hills. He was using regular grade gas. He immediately switched to premium.

What's the danger of significant damage to the engine from knocking? Should I walk from this car? I do not know how long he drove with lower grade fuel.

Thanks in advance.