Till price vs Shelf price

Some few years ago I wrote to Clicks regarding the fact that the pricing on the shelves did not always match the pricing at the till (and not in favour of the consumer). I received an explanation and was assured that this should not happen again. Well it has happened on numerous occasions since and the last time it was at Clicks in Greenstone. The price on the shelf for L'Oreal hair mousse was R108. but when it was rung up at the till the price showed R120. This is a R12 difference which is really unacceptable. I make a habit of checking shelf prices before I purchase goods but what about the number of customers who do not do this? It would be interesting to have a survey done. In this computerised age, surely this should not occur.