The article missed some of the most famous tricks. Friendly’s restaurants would just come out with a new menu with completely different items on it, so there is no way to compare portion sizes or prices.
In 1980-81, I worked in a Pizza Hut and read the managers’ guides during slow periods (Tuesday evenings). There were explicit rules for cutting down on salad bar consumption. Plates instead of bowls, or, if bowls are employed, make the bowl itself small with a large lip to force repeat trips to the salad bar and make customer feel like a pig. The sneeze shield is purposely placed low, with the cheapest food easiest to reach. Food containers are also to be shallow (who wants to take the last olives?).
This was in 1980-81 (still feeling the effects of Carter), so restaurants playing games is nothing new.
It’s as old as time. In the 1800s milk could be watered down and even contain chalk dust. Soap could be substituted for cheese...