Must be a location thing. I've never been to a store selling <$100 shoes (the kind the OP was shopping for) that didn't have all or most of its inventory on the shelves. For higher-end stores, yes the space is often devoted to display with inventory "in the back", but I was just at a mall Sketchers a few months ago and found my shoes myself with no problem. Same with my department store shoe sections.
Replying here--yeah, the stores inside shopping malls typically lack the real estate to have all the shoes available in the main store and, instead, keep them in a stock room in the back. I've definitely been to both types; but, the mall stores are almost always the "pick a display shoe and have a salesperson bring your size."
