Calling them on lies

I'm just wondering if you call you person on their lies. I'm not talking about huge life changing ones but everyday smaller incidents. We have been having issues with our furnace. The technician said it is because the filter isn't cleaned enough. I can remember one time my DH cleaned it. He swears he does it once a month. Such a huge bald faced lie. I cannot even believe that he would say that. What do you say in these kinds of instances?