I have actually gotten shipping notifications from Amazon when I placed the order on eBay.

Several times I have purchased an item on email only to have it arrive from Amazon. The sellers were using both sites and there was no way to tell from the eBay listings. Big sad.

This instance might help you: https://lemmy.world/c/keeptrack (Someone else doing similar.)

If it’s their original thought, or I’m including their comment on the thing they shared, then I include the username.

If they’ve just reposted an image with no extra commentary, I only share the image and not where I found it. Since “where I found it” is not the original source, no attribution is necessary imho.