Aaron Berk's latest 'podcast', #71 has a great infographic (29:36) of how to use the proper codes to avoid getting hassled. My first package from Europe (via FedEx, and first since the de minimis chaos of September) went into customs purgatory but luckily I had a nice agent. I'm not sure if it was my letter explaining the contents or if it was the code which Victor Clark had mentioned in a post, but the coin was quickly released. I didn't have to fill out any forms. #3299 must have been a mistake. Here's the video: