When an AM station is ran correctly, it can sound pretty close to FM. When the station uses up it's bandwidth efficiently and provides the whole range of spectrum instead of a narrow slice, and when the station uses a proper modulator, and when the station tower is the right height, and whatnot, the station is ran correctly. Also of course, you can tell which stations are good quality because they can still be readily heard in their fringe areas, or even outside of them (this last statement mainly applies to plains stations like KRVN).