Exploitative prices and bad customer service

My 75-year-old mother visited the Lonehill Shopping Centre's gadget Paradise branch to buy some batteries for her car remote. The store assistant advised her that the tiny batteries she was looking for were R70.00 each! She remarked that this seemed excessively high, but he advised her that they were superior quality and that she would not find a better deal anywhere else. Being a kind, yet naive elderly woman she assumed he was being fair and honest, and desperately needing the remote to work, reluctantly paid R280.00 cash for the four CR1220 batteries without receiving a receipt. On returning home and complaining about the price she paid for these batteries and how she could ill afford them as a pensioner, I helped her to do a price check online only to find that the price for the exact same battery was R15.80 (R79.00 for a pack of 5). On returning to the store the following day, I explained to the store assistant that I felt he had taken advantage of an elderly woman and that the exact same batteries were MUCH cheaper elsewhere and asked him to consider giving a refund. He explained that my mother accepted the 'first price given' and suggested that she could have negotiated a lower price. I objected, explaining that in South Africa we generally assumed the price quoted was not negotiable, and told him that I felt this was 'taking a chance' with an oblivious desperate pensioner and requested a refund. He blatantly refused as he said that she could not produce a receipt for the purchase and that she had not refused his first price offered. I find this stores' conduct extremely exploitative and unprofessional, not to mention that one would expect the management of Lonehill Shopping Centre to lease spaces to companies of a higher caliber. I would advise any future customers to be extremely cautious and first seek alternative retailers when considering this store.