Sorry to hear of your travail, but you have recommended the best remedy. I always note whether my non-smoking preference is "guaranteed". If not, I cancel. Sometimes, you can get your smoking preference by changing your bed preference. Said differently, perhaps they have no more NS Kings, but they have NS w/ two double beds.

I agree that they could do a better job of highlighting that your prefernce is not available/guaranteed. Importantly, Marriott does a poor job of telling me which preference has not been guaranteed. If it's the bed type, I can probably live with it. If it's smoking preference, that's a deal breaker. Only by fudging the preferences can you find out which is not guaranteed. On that, I agree there is room for improvement on Marriottt's web site.