Generally speaking every time the USPS increases rates there may also exist certain variations in price between the ounces for first class. For example, before the increase a first class parcel weighing 8 or 9 ounces cost the same, now it does not (now 9 ounces is like 50 cents more).
May or may not make a difference but in my case with 100+ listings in at least a few instances it does.
And then they "revert" back to the old prices in a few months but just for a short while and then back to the new.
The slick 1-2-3 oopsie money grab.
