Wrong pricing at Checkers

It seems that from all retailers Checkers is the one where one has to check the prices on the slip most carefully. I experience all the time that the prices on the slip are not as priced on the shelve or as advertised. But I find it even worse when the management blames the customers before checking properly. In my case I was told that the customers often don't check the correct prices. I always do that before I complain and also in this case I got my 20 Rand back which I was overcharged for the cooking oil. Unfortunately I realized at home that I was also cheated by the pork meat which was on special at R88/kg instead of R130/kg. I asked the lady at the butchery how that works with the special price and she explained to me that I would pay the amount as it is stated on the packet but they would deduct the balance and I would see it on the slip after I paid. One must have mathematic skills to check if the price is correct. I worked it out at home and found out that I was charged for all 6 packets the wrong price and was cheated by close to R40. I don't think that everybody checks the slips at Checkers all the time but one really should as they make their extra money. How comes we are never undercharged? Isn't it strange that the wrong price is always in their favour?????