I wonder if it is very unusual for an animal to understand quid pro quo.
One thing's for sure - it's really cute.
Dogs definitely understand habit. So if they waych an exchange, they caretainly can figure out how to participate in exchange.
I heard of one that was given a dog biscuit for fetching the newspaper. He began taking the neighbors' newspapers & stashing them in his bed. He would bring one out when he felt like having a treat later on.
I'm sure he could have gotten a cookie by just using those big brown eyes.