They aren't "pre-paid" but rather "we will pay the postage, provided you return the envelope". I.e., the PO charges for the count of what comes back through th

They aren't "pre-paid" but rather "we will pay the postage, provided you return the envelope". I.e., the PO charges for the count of what comes back through the mail. In the U.S., the postage cost is full first class rate plus a service surcharge.