Wrongful advertising

They had a 50% off sale running and the one dining set I was interested in had a 50% off sign on it. As advised by the sales lady in there, everything that had that board on was on promotion. When I came back to enquire about the set, I was told the board was put there by mistake (probably by kids coming in and out of the store) and that it was not on special. Shouldn't the customer pay the price they see? After complaining at head office I was only offered a R1000 discount on the set :(