That's supposed to be one of the benefits of "outside" shoppers, as opposed to "corporate quality checkers". Every company I've ever worked for who had corporate checks knew ahead of time exactly what day the inspector(s) were arriving. And STILL couldn't get their act together!
When I was working for Pizza Hut (before I was injured at work in May, 2015), I dashed into the ladies' room one night to wash my hands. The sink was BLACK. I went and told the manager, and offered to go clean it.
She said, that's the waitresses' job, they'll clean it. I said, are you sure, the corporate inspectors are supposed to be here this week; she said MYOB.
When the inspectors came, they gave perfect marks except for one item -- they said the ladies' room sink was filthy.
I still chuckle when I think how stupid that boss was.