Thanks @karencarrens I am really into dog psychology and their way of communicating and experiencing life. Our dogs are rescue dogs as well. Of course he saw the food as the rewarding. Dogs love to 'work' for you, but they even like to work together more. One of my dogs almost know every 'command'. People use to say that there is no chance that he can like that, following commands. My question in return for them is; if I'm always nice to you, help you whenever I can and always approach you with respect, would you slam the door in my face when I would nicely ask you: 'please, can you hold the door open please?
Their facial expression is al I need at that moment :)