The packing slip had two one-dollar bills taped to it, and a handwritten message: "$2.00 Shipping Refund - Amazon's system is allowing to[sic] much for shipping - partial refund".
Well, hey! They just earned some positive feedback.
How do I give it, though? Amazon has in the past emailed me saying "Leave feedback about these sellers", but I haven't gotten such an email yet this time around.