I was going to say: I think there’s a mixture of customer selection and signaling from management going on here. I think Costco (and all stores really), subtly signal how their employees are to be treated, which creates a norm and a social expectation that most people implicitly follow.

I think the fact that Costco employees don’t have to wear a full uniform is part of it. They have a clear identification that they’re an employee, as is necessary, but they also don’t have to wear a uniform that strips them of as much individuality as possible.