While the USPS slows down from Thanksgiving to Christmas, they also hire extra staff. (Okay- deJoy is still in charge. Thanks trump.)
Sellers who usually use untracked LetterPost and Small Packet USA may want to upgrade to Tracked Packet USA which is tracked because in a Not Received dispute, entering the tracking number, even if it does not show delivery, may lead to a small extension in delivery time to allow for receipt.
Sellers can also add a longer Handling Time or advertise a slower service and upgrade to a faster one, whether we eat the difference or add to our Flat Rate shipping/ handling charge.
Remember that on many services the shipping cost the buyer sees is the counter rate, not our discounted cost.