These are in the classifieds and they are the original poster's own auctions, so yes, it's generally considered bad form to promote one's own auctions through the classifieds without at least offering them directly first. For instance, what I usually do is put something up here, and if no one is interested, I might post it on eBay after a week or so and add a link to the auction in the original thread and say "moved to auction."
Posting a heads up about an auction you've seen and have no connection with is okay, preferably in this thread--
(there was a url link here which no longer exists)