Asking a higher price is within the seller’s rights. A shop does not necessarily have to sell you anything, or at the price they have displayed. Showing a lower price might be because they have made a mistake, forgotten to update the tag, or they might be trying to invite you to come and open a conversation with them. But incorrect price indications can be an offence. If you think the shop is deliberately misleading you, then you can report the case to the CRC.