Calling customers, "guests". A customer is someone with a business relationship with someone/something else. They're exchanging money for goods and services and have a right to expect certain value for their money.
A guest is something else entirely. A guest has no implicit right to expect a certain any particular level or quality of services. They are dependent on the magnamity of the "host".
Calling a customer a "guest" robs them of status.
Take a look at this:
This is in the Museum of the Palazzo Massimo alle Terme in Rome, and it comes from an ancient Roman Villa in Rome. Probably painted in the first or second century CE. There's walls of this stuff in the museum.
It's not realism, but minimalistic sketches that, in many ways, outdo realism in artistic quality. To me, this looks more like something that you might find in Leonardo's sketchbook than on the wall of on ancient Roman Villa from 1200 years earlier.