Put the crowd sizing advice directly under the size picker

What it is

Directly beneath the size grid, one plain line says "Most customers choose a size smaller." It is not in a size chart, a modal or the description: it sits where the shopper's eye already is when they choose.

Why it works

Fit doubt is the main reason shoes go back, and a size chart asks the shopper to do work. A one-line recommendation drawn from what other customers kept removes the guesswork in the place it happens. It is only worth shipping when return or exchange data backs it; an invented sizing line just moves the returns around.