Recently while doing artifical wall climbing I saw some Pro's wearing shoes which were a size smaller than their actual shoe size , was interested to know why is it that they wearing a size smaller and got the following Info

Rock climbing shoes are likely to stretch over time (mostly in lateral width), while lined and synthetic upper shoes are not likely to stretch much at all.

Climbing shoe sizing varies from brand to brand and, just to confuse the issue, often from model to model within a brand. Use numerical sizes purely as a guideline. As a rule of thumb, the level of shoe discomfort increases proportionately to an increase in climbing "level". This is primarily a result of molding the foot into as firm and precise an appendage as possible in an effort to eliminate "roll" (due mainly to weak feet or the shoe being to big and rolling around your foot) and increase sensitivity (sensual feedback) and pin-point controlled.