The person at the door was very diligently checking. This was the SF Costco, in the early days of the pandemic lockdowns, so perhaps it's unique to that specific location or those specific circumstances. Indeed, just a few weeks ago I went to another Bay Area Costco intending to inquire about membership, and the person at the door was just handing out promotional flyers, so I helped myself to a quick self-guided tour of the store to see if I thought membership made sense for my household (I did decide to buy a membership, for what it's worth).