[dagw]

Some sites online offer actual, specific measurements for all their clothing instead of vague sizes like "6" or "10", whose meaning isn't even constant for a given manufacturer. I've never seen anything like this in a physical store.

But at a store you can simply look the item, and if it looks like it should fit try it on to see if it actually does fit. The actual size printed on the item isn't that important in those cases.

The other aspect is that stuff like stitching, button holes, collar construction, and general feel and quality of the material used is incredibly hard to judge online, while trivial to judge in person. Stuff like this simply doesn't matter when it comes to books and electronics.

Of course all these problems are solvable, but it is a much much harder problem than selling books online.