I agree with you 100%, however, what would it cost you to fight them over it? My guess is more than the total amounts due, not to mention the time and effort. That is why they can get away with it.
Think about it this way as well. What is minimum wage in the US (as an average anyway)? Now look at you $6 shops and how much time you have to prepare, commute, spend time there, write the report. Lets just say it is 2 hours ( and you must count all time spent), that is a rocking $3/hour. They can get away with breaking the law on that by making all shoppers IC's. Now, they can violate labor laws and get away with it because we are allowing them to do so.
Fixing issues like this or trying to get changes in process cost time and effort which most people are unwilling to give the effort needed to make changes, for various reasons.