Socks Pet Peeves
It might make inventory more expansive, but offering socks in multiple sizes, each with a limited range, is usually a better idea than one-size-fits-all.
When I see socks labeled as one-size-fits-all or simply men's, I know they won't fit me. When you have small feet, which I do, finding any sock marketed to men that doesn't result in the heel lining up with the top of your ankle is incredibly time-consuming.
One-size-fits-all is really just saying that the sock will fit the largest size listed, but they want you to buy it even if it doesn't fit. Sometimes, they seem like they might fit, but then you realize that they will not once you pull them on tightly, and if they did, they certainly would be a poor fit for the rest of the range.
Disclaimer: I wear a size 7D (US).