They deliver it postage due. "Someone" in my local post office must have a lot of time on their hands, because I have had several chips with printed postage show up with POSTAGE DUE stamped on them and a coin envelope for the difference, if they were mailed at something less than the first-class parcel rate. Needless to say it's a big hassle for both me and the shipper.

As far as I can tell, this only happens to ones where the amount of postage is printed on the label. Some online-postage places offer the option to hide the amount of postage paid...problem solved.