1991 GMC Jimmy white smoke

I bought this car a week ago or so off craiglist from this man he told me the only thing wrong with it was the brakes said it, s never keak oil or burnt it so went to look at it to it home week goes by it start to smoke when you start it only white alot so I call the man told him I need a smog so he had me take it to his menchanic I know it wouln, t pass a smog leeting that much smoke out when I go to pick up the car the mechanic said it pass I asked about the smoke he it was condesnation and he had drill holes in my muffler to let it out started it was still smoking the mechanic it was because it has worn valves I don, t know what to do but I think the owner knew should I confront him or is it a fixable thing