On my third attempt, I reminded them that I'd like to leave positive feedback if I can. I received this response:
Thank you for your purchase.
This order did not go out yet. There is a chance that it was misplaced in our inventory (we stock several thousand items on our shelves). I did personally find the order, pack it and ship it yesterday (Tuesday). You should receive it tomorrow (Thursday). It shipped via USPS Priority Mail.
I really do apologize for the inconvenience. We sell a lot of misc. surplus equipment (I have approximately 5000 listings on eBay). And stuff like this can slip by me sometimes.
We always try to avoid negative and/or neutral feedback (since eBay counts neutrals as negatives now). If you have any further issues, please contact me directly.
Feel free to call or email if you have any other questions.
This puts me in a quandry. I don't buy their excuse, since I did repeatedly contact them. On the other hand, I know that eBay is charging higher fees for vendors nowadays when they receive negative feedback. I don't want to discourage people from using eBay, so perhaps I'll just decline to offer any feedback. Sigh.