[ballenf]

The membership checkers are there to give members the feeling of exclusivity and belonging. They do not generally turn people away and will accept basically any reason from "meeting someone" to no response at all, in my experience. But I haven't been to more than half dozen Costco's, so can't speak broadly.

[raisedbyninjas]

I think their primary purpose is to ensure that nobody who isn't a member or forgot their membership card gets in the checkout line and slows it down.

[ceejayoz]

I suspect "where are you going with that $2000 TV?" plays a role, too.