Our friends had been in previously and had been overcharged for the house wine (on offer until 6 pm as per the blackboard above the bar), on that occasion they didn't say anything but when we went in this time she specifically asked for house wine. It was their previous experience that prompted us to check the bill.
Maybe they need to look at how specials are shown on the bill. Like others on here we like Shaka very much - the staff, the ambience, the food and the setting.