I also like delbert's idea. Make sure you bring with you that pic of your son and a picture of the outside of this guy's business. PLUS... if you can find 2-3 more people who have had this same experience, add their names and stories too. You may even want to call your local TV station because they LOVE stories of children getting taken advantage of- I know that sounds bad, but they do. I know my local station would have a hay-day with this and they would do a full-out investigation on this guy and his business. He'd be hurting for money for awhile.
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!