Dogs are really good on picking up human behavior. So much so that they can recognize a liar and it's proven by science.
A team led by Akiko Takaoka of Kyoto University in Japan did a study which discovered that dogs actually know if you can be trusted.
In this study, they essentially tricked dogs in the name of science. During this experiment, a person would point to a container and the dog would run to it and found hidden food. It established some trust with the person.
Then they pointed to an empty container. The dog ran over to it and found no food. The third time they pointed to a container that DID contain food, the dog refused to go to the container. The trust was broken, they knew because of the last experience the person wasn't reliable.
34 dogs were used in the experiment, and every single dog wouldn't go towards the container the third time.
So the lesson here is DON'T LIE TO YOUR DOG.