Whatever you do, don't buy over the internet. Trust me, I went to Outside, and tried on:
5.10 Anasazi Velcro size 9, a touch too big.
5.10 Anasazi Velcro size 8.5, a touch too small.
Finally, a different pair of 5.10 Anasazi Velcro size 9, perfick!
When they cut the material they get lots of layers and the machine pushes a big template downon it. First layer gets cut, but the last layer gets squashed. The layer on the very bottom, get squashed, pushed out, and then it gets cut. Hence, when the material is not being squashed, the overall cut is a bit smaller. It's more noticeable in rock shoes, but it happens in all of them. If they have two shoes, both of your size, try them both. One might fit a touch better.
Oh, and anyone who thinks about buying rock shoes, without trying them on a bit of an indoors wall is mad. They should have some tiny features (or coins like Outside in Hathersage), for you to stand on!