How do you know if your kid is faking being sick/has your kid been a faker?

What exactly are his symptoms? To me, its hard to play sick, in my house if your over kindergarden, you may not miss school unless you either have a fever or you throw up, both are not really something you can fake considering I need to actually see the puke and watch them with thermometer. If they are kindergarden or below, they can also miss if they have a really bad cough and a super snotty nose (not just a normal cold, but a hacking up a lung cough), both of which are also not easy to fake. None of them has ever played sick. I dont know if picking him up early is a good solution, it might give him the idea that playing sick will get you to come get him quicker which could make it a habit.