In EU countries there are often advertising regulations to the effect of sale prices having to be lower than the average price of that item over a certain period leading up to the sale, you can't raise the price right before a sale, etc.

Discount codes are widely used to mitigate this though. Lot's of retailers in the UK have a sales every few weeks and when there isn't a sale they have discount codes.

That's not at all what I'm describing. Whether our old policy of selling for half the average retail price, or tagging it at full retail but giving 50% off at the register, we were selling for half what the customer would pay in any other store for the same merchandise.

What you are saying is the opposite and is extremely immoral (and likely illegal in some places).