Many "commercants" have called for the January sales to start on 2nd January, a week earlier than usual, to try to make up for the loss of trade caused by the gilets jaunes actions. But prefectures have declined to advance the date on government advice. Many shops will nevertheless have "private sales" or other special promotions. Generally French commercial law does not allow sales outside the designated periods, nor the use of "loss leaders".
A salesman we talked to on Boxing Day (26th December) was surprised to hear that day was a holiday in the UK and that some 18 million people were going to pass it at the January sales.
** We are reminded by a non-pedantic reader that Boxing Day is not a UK holiday, as it is not celebrated in Scotland. On the other hand, January 2nd is a holiday north of the border where they will still be trying to recover from Hogmanay.. But happy New Year wherever you are.
