I wear a 10 and I ordered a 10 M they fit fine.  The problem with this sandal is and to me this is major.
I would like to know what the hell the insole is made of?  The insole is as hard as cement and has marking or indentations I guess to keep the shoe adhering to the foot.  Whatever the reason for this, the uncomfortable insole
makes this sandal not comfortable at all.  I'm glad I didn't pay the asking price, for I would have been totally pissed.  Now I've got to find another pair for I sure as hell can't wear these for any length of time