I ship very few chips compared to most folks, I also use non-machinable surcharge stamps but with #000 bubble mailers, So far I've never had one come back to me marked postage due or heard of a recipient having to pay additional postage on their end. I think the key is I drop them off in the mailbox in the parking lot of the post office rather than taking them inside to the counter where the postal employee inspects the package and deems it to be a package costing almost $4 for postage alone. Another thing is if the recipient does want tracking, I use a 3rd party shipper such as ShipStation through PayPal where you get a small break on shipping costs...