UPS

Every UPS store that I have been to have their shred box is out in the open. This UPS store has it in the back. A customer never sees it. I brought documents to be shredded and the woman disappeared into the back of the store out of site. When I told her that I didn't want my documents put in the shred box out of site, she told me that customers are not allowed in the back of the store. What are they hiding? What are they up to?
It is very suspicious.