Would lawnmower with bent crankshaft still start? And run sometimes?

We brought our lawnmower in because it starts and then shuts right off and it is still under warranty for another week. They said the crankshaft was bent, but the only thing we have ever hit that stopped the motor was about a year and a half ago. Also my brother helped us get it going and it was running fine for about ten minutes before we shut it off thinking it was fixed. Would it work at all if the crankshaft was really bent? We have also had it serviced elsewhere for the same thing and they never mentioned the crankshaft, they said it was the carburetor, it was dirty because our yard is so dusty. They cleaned it and it has been fine until now. I just don't get how if it is basically junk my brother who is not a mechanic of any sorts could get it running.