Dollar Tree review: service

I went into the dollar tree in wadsworth for my child to pick out a toy as a reward for something he had done. We go through the store and he picks out a toy that he is so excited about. We get to the register and the item rings up as an unsellable item and they will not allow us to purchase the toy. Why would you have items on your shelves that are for sale that you are not actually allowed to buy?! How do I explain that to my heartbroken child that your store won't allow me to purchase the toy that he found on your shelf that was still in original packaging, unopened?! The clerk who was ringing us up was very nice, but the manager was very rude and did not even apologize! That was the worst customer service / experience I have ever had trying to shop at one of your stores.