I was wrong, missing a couple small parts. F-it.
At the beginning, the packages arrived with USPS stamps, but always 15 to 21 days after the order was placed. My guess is that they send a bunch of packges in low cost carriers, then somebody in the US separates the boxes and stamps them for US domestic shipment. As I increased the volume of each purchase, later orders arrived in boxes stamped directly using Thailand Postal Service.