I needed to be sure before purchasing these on line. So I went to a shoe store and asked to try 2 different sizes, in both widths. And even after that, I'm not convinced I picked the right size for my feet as I may have tried the sandals in a bit of a hurry. Note to self: never make that mistake again.
But now the shoes have molded a bit better to my feet, I've been thoroughly enjoying wearing them :-)
Dec.2012 edit: in hindsight, I should've gone for a leather material as this is starting to have little cracks where the forefoot folds by the big toe. Time's taught me.