What is a 'bad conversion'? do you mean a low percentage of conversions? if that's what you mean, then the answer is no.. Adsense wont ban you, they'll SmartPrice you.. a fate almost as bad as being banned..
No, Adsense doesn't ban people for conversions (clicks) from non-US based visitors (like Yahoo does). The only reason they will ban you is if you are breaking ther Terms of service or for fraudelent clicks. If your sites don't convert well you will be smart-priced, but that only means you will be getting paid much less for a click.
Smart pricing is IMO just as bad as being banned.. They make it virtually impossible to make any money with them.
Smart pricing only comes into effect when you have really bad conversions. If you have a site that is not doing well, then either take the code off that site or tweak the placment of the ads until you are generating clicks and the smart pricing will go away very soon.