IIRC, there is a way to do something similar in with the USPS, even if it is just a simple letter. Fill out a form, and the receiver gets a bill for the postage due. Something similar happens if you post a letter that cannot (for whatever reason) be returned: The receiver gets a bill they must pay before they can have the package.
I think that they figure the sender probably knows they are getting a lot of mail since the bulk of it is items ordered. They can know they are non-compliant by having standards on how many "free" packages one can receive and/or sending a notice when one is getting close to the limit.
I think that they figure the sender probably knows they are getting a lot of mail since the bulk of it is items ordered. They can know they are non-compliant by having standards on how many "free" packages one can receive and/or sending a notice when one is getting close to the limit.