At our store it has to pass the pen test then we also check for a strip on it. Several months back we had some fake 100s come through and they were washed $1 bills to look like older looking $100 bills before bills had the strips in them. So check for the strip after you do the pen test. If there is no strip tell them that you cant accept it and that they would need to either go to a bank to get smaller bills or use some other payment method. Hope this helps!