I'm like you, sons & daughters that I was going to stay out of it because I am a non sewer. I can do a bit of hand sewing, that's it.

My take on it though is that you wouldn't buy a second hand machine on ebay unless you did sew and if you did sew, you'd probably have a close look at the photos in the ad, to see what was included and what condition the machine & bits and pieces looked to be in.

The ad specifically says-accesories as shown-including zipper attachment.

To me, that is always a hint that you're only getting the accessories shown in the ad. You're not necessarily getting every  accessory available for that thing, whatever it is. It's a second hand machine so you can't take it for granted that every original extra will be there.

The time to google and find out what this machine originally came with and to ask questions about anything not in the photos was before buying.

I feel for this seller because I remember once my sister & I sold something-I even forget what it was exactly. We took clear photos of it. We never implied there was anything else with it. It was something like a wine decanter? I forget exactly. 

Then the buyer later said they expected such and such to come with it. Something totally unrelated (in our minds). My sister just replied and said had it included that, we would have mentioned it and added a photo of it.

We were not intentionally misleading anyone. I don't believe countrygirl was either.

Unfortunately, the waters have been muddied by all the later messages about selling the extra bits.

Personally, I would not refer to those again, just keep any discussion to the original transaction & the fact the ads said accessories as shown and there were several photos of what was included. And that the buyer receievd absolutely everything in the photos. That the pieces she is complaining about as missing were never mentioned or shown in the original ad.