Counterfeit Bills

Who keeps passing counterfeit bills in my store?! STOP IT. You're really making me mad. Because every time you do so, I get in trouble from my boss(es), despite my employees being trained and having used the standard methods for detecting a counterfeit--hold the bill up to the light, look for the strip and watermarks, check for color-shifting ink, feel the bill for the right texture, use the special marker on it. What more can I do?! I'm not the Secret Service or the FBI.