We look for ways to exert influence or control over a situation.
Our level of stress declines and feeling of certainty increases when we perceive greater autonomy. How larger the group, how larger this urge to make our own choices. You can introduce - even trivial - choices by introducing customization options. This can be applied to the product you sell (color, form, print, gift wrap) or your shop itself (different fontsize, another stylesheet).
PS: don't offer too much choice to prevent Choice Paralysis