Alays a problem with pricing

Almost every time we go to the Newlands spar in Pretoria we experience a problem with there pricing. The sweetcorn rang up at R6 more than the shelf price (R18.99 instead of R12.99). When we bought this to the managers attention she said that this was for a different brand. However this was the only price on the shelf. She then offered to refund R1 for the potatoes which were also priced incorrectly (seriously)?? This manager clearly has not got proper customer care or managerial skills! R6 is obviously not a lot of money however I would like to know why Spar feels the need to constantly 'trick' customers in terms of there pricing?