Clerks help run your store. You can change your clerk at any time, and there's no limit to the number of clerks you can own. Each clerk has a different personality, which in turn has different effects on your shop.
Clerks with high intelligence gain knowledge faster, meaning you'll unlock new perks in no time.
Clerks with high friendliness are better hagglers, meaning that customers will lose patience slower and be easier to bargain with.
Clerks with high salesmanship generate bigger sales, meaning you'll rake in more cash.