My late Dad for years used those one gallon square gas cans, would always keep one in His vehicle and bring home another gallon of gas every time He went anywhere, and find something that needed "Topped Off" around the house.
I remember Dad always bought His gas from a little country quick mart out in the sticks. One day Dad was filling the little can, gas was $2 per gallon, and He stopped pumping when the pump showed $2.50 and the can was not full! He went inside and said "That pump is not right! You cannot put $2.50 worth of gas in a one gallon can!" They told Him, "Sorry, but that is a "Legal Sale". You owe us $2.50".
When He told me, I said "Dad, I would not trade with them no more". Dad said "But that's just crazy Son! I can't do that!"
I asked Him "Why?"
Dad said "Son, they have the best 25 cent fried chicken wings on the river. I can't let that go".