It should not matter. If they want to charge you for something that is not correct then ask to talk to the postmaster and show him a printout of their own rules. The same rules (that they make) have to apply to everywhere.

That's what I eventually thought was the answer.

If I measure and mail and it's correct, then the receiver needs to go to the office and ask why they added fees for a mailing that was done properly.

If it's wrong, then I understand and the seller/shipper should make up for their error.