I read another review that they ordered 7M  in these and the left was bigger than the right.  I had the same problem.  Left shoe 1/4" too big, right fit perfect.  I wear an 8W in most shoes. The right shoe fit perfect, but left too big.  I put the shoe toes against a wall, took a ruler across the back of the heels and the ruler doesn't touch the back right heel.  I then measured each shoe from it's longest points front to back, the left 1/4" too big, leaving a nice big gap between the strap and my heel.  Sent them back for return, no exchange.