True...but some of those were butchers, etc. where it was done for hygiene purposes.
OTOH, my mum worked in the Co-Op from the age of 14. At 16 she was trusted as a cashier (ca. 1944) and worked at the end of one of those vacuum tube setups (and, on bad days, in the 'overhead wireway' booth in the basement where theer presumably wasn't enough 'suck' to get stuff to the cashiers' office on the top floor). That may have been mistrust of the shop floor staff, or simply security.
Of course, she *had* to laeve when she had a child (me).