A customer recently returned a grip adapter by using the Priority Mail flat rate box that was used to deliver the adapter to him, but he only put Media Mail postage on the package. I managed to talk my local post office out of returning the box to sender for inadequate postage, but promised to post notifications on the web site and elsewhere so it didn't happen again.

SO - it is UNLAWFUL to use Priority Mail shipping supplies provided by the USPS (which is what is used to deliver ALL BK grip adapters to customers) UNLESS YOU APPLY PRIORITY MAIL POSTAGE. Failure to apply sufficient postage will result in the package eventually being returned to you, thus causing loss of the original postage paid and delay in receiving a refund for the return.