It is incredibly unlikely that a car not intended for the US market would meet US safety and environmental standards as they are highly specific. For example, a Mercedes bought in Germany might not meet US standards because it built to meet European standards. Some Chinese car manufacturers have looked into entering the US market, but so far they fail most standards. Even if Chinese cars were perfectly safe and relatively clean, they would still need to be redesigned as they would be built to the specifications required by Chinese authorities which might be at odds with those required by US authorities. For example, they might require different colored lights on the cars for different indicators, so all the lights would need to be replaced.