In relation to the price on "sale goods", to allow the sale price, the law states that the goods have to have been on sale at the higher price for a period of 28 days in the proceeding year.
Hence, the prices are artificially raised up from 1st December to end December, as nobody buys during that month, so that it can be dropped again on 28th December, when sale starts.
So something which cost €600 all year may rise to €1,000 during high price season, to be put back to €600(or slightly less) to make it look like there is a massive saving of €500, when in fact there is not