I wear a 9.5 in regular shoes, but a 10 in Crocs.
I tried the size 10 Mary Janes on and found them to be a bit too large, but the 9's were too small.
If I was going to buy them, I would have to wear the back strap down on the sole since it was too floppy with it on (kind of like a more feminine version of the clogs).