I've read online women claiming that occasionally clerks in shoe stores will swap out different sizes in a box for them when their feet need two different sizes. That's what they claim anyway.
I was surprised at the number of amputee shoe-swap web sites that came up when DH and I had a discussion about it. One of the beauties of the Internet. Can't imagine how difficult special shoe needs were before the net.
Respectfully, bull on clerk size swapping. No shoe salesperson would ever do that-they’d be canned on the spot. Customers do it all the time but it’s gotten much harder to get away with as sizing is supposed to be checked by both the salesperson and the cashier.