When I was younger, and what I heard from my mother, so my information is from about 1940's in Brooklyn, you trusted the proprietor of a food establishment to police himself. You were relying on his yiras shomaym and knowledge of halacha.
the corner luncheonette, the butcher, the takeout place.
It was only as establishments wanted to service customers that didn't know them that formal hashgachas became so established.
So I guess I'm disagreeing with the premise of that Kol Koreh.