Re: "trying on shoes in a shoe shop"
Different manufacturers use different sized lasts. And plants on different continents belonging to the same manufacturer use different sized lasts. The only the only good way to purchase shoes is to physically try them on.
Last time I bought "walking the dawgs" shoes, I tried on four identically labeled pairs. One pair was too small, one too big, and two fit. I bought the two. They were made in Mexico, the large pair was made in Malaysia, and the small pair was made in Taiwan. Caveat emptor.