What you're talking about is a "shopping service" of which there are lots of different ones out there. (I was a mystery shopper for KFC for 3 years in the 80s). During that time I remember flying on TWA and the flt attendants commenting that they could always tell when they were being shopped b/c the same person did an out/back trip (e.g. STL-BNA and then right back to STL).

Search for "mystery shop" and you'll see some of my war stories
jl