If there is "buyer beware" is there an equal "seller beware"?

Is seller beware the same as buyer beware? My neighbor had a vehicle that was overheating on him and he said throwing water out of the tail pipe and bellowing smoke (the classic blown head symptoms). He knew I was in the hunt for a vehicle since the last failed to pass smog with out expenses near equal to the value of the vehicle. He said if I was willing to repair the head on the engine he would sell the vehicle to me for $150 bucks. I thought if the leak in the head was not bad I could repair it with a professional grade block seal and have a running vehicle for a fraction of the cost and a little TLC. I started the vehicle and did not see the tale tail symptoms (then again I did not run the engine that long, just wanted to see if it started). It did not have to go far so I drove the vehicle to my home. Upon checking it out it never got hot when I ran the engine or seen any water and smoke thrown from the tail pipe. There also was no oil in the water or water in the oil. I even drove it to Ace to have an extra key made, never any sign of over heating. I am thinking maybe it was another cause or a sticking thermostat that was causing his over heating, and not a head gasket. Should that be the case should I tell him and offer him more money or since he was so sure (so sure at one point he tried to talk me out of buying it) it had a bad head it was his misfortune in misdiagnosing the cause of the overheating and way under sold the vehicle? They always say “buyer beware” does the same go with sellers?