No refund on incompatible HP printer cartridge, recommended by Hi-Fi Corporation in the Secunda Mall.

My wife needed a black ink cartridge for our HP printer and elected to purchase one at Hi-Fi Corporation in the Secunda Mall. The sales assistant advised her that they don't have the requested cartridge (HP 652) in stock, but they do have a HP 653 available, He assured my wife that it would be compatible with our printer. The HP 653 cartridge was then purchased in good faith based upon this assurance from the salesman. Upon installation at home however, our HP printer gave an error message that the cartridge is not compatible with the printer and therefore unusable. When my wife returned the cartridge to Hi-Fi Corporation in the Secunda Mall, where it was purchased less than an hour before, they blatantly refused to refund the purchase, claiming that the package had been opened... Seriously...how else would we have discovered the incompatibility problem without opening the packaging and installing the cartridge in our printer? I am now R429 out of pocket and stuck with a printer cartridge that I cannot use, all because I trusted the "expertise" of the salesman that assured my wife that the cartridge would work without problems in my printer. I am extremely unhappy and dissatisfied with this level of customer service received from Hi-Fi Corporation.