-MIKE- wrote:

Again, how can you deceive someone by clearly labeling exactly how
much is in the jar? I'm not aware of any law requiring mayonnaise makers
to sell it in quart jars.

I wouldn't exactly call it "deception", more like "they won't notice a
slightly smaller jar so we can give them less for the same $$". Sure,
people can check the unit price but most people would never do that for an
item they buy regularly. IOW, the sellers are hoping their customers won't
notice a slightly smaller package. Deception, no; sneaky, you bet.

At least the potato chip folks have the "Contents may settle" admonition on
their mostly air filled packages.