Incredible Connection 15% return policy fee

I went to Incredible Connection Sandton City to buy a tp link Wi-Fi extender in March which was on special for R1399), and I was encouraged by the salesman to buy a Xiaomi mi ac1200 Wi-Fi range extender (R1499.00) because it was more advanced and easier to install. The IT guys I got struggled to configure the extender to work. Within a week I returned the extender to Incredible Connection and I was told that I will be charged 15% return policy fee. This was not communicated to me when I bought the extender and I feel that such information should be displayed for all customers to see so that they know what to expect. This is the 1st time that I was charged when returning a product. I was very unhappy and shocked that such an amount would be deducted since nothing was damaged or dirty when returned. I will not be spending any more money at this retail shop.