~~~ if I can either end an auction early (if there are no bids) in order to sell my item to someone who made an offer -- or if I can make an offer on an item I'm interested in; and their reply (all in the archives; as I've made mention of this several times) was always that they have no problem with the practice, and informed me that I would not be able to leave any feedback.

I have not done this in a few years, so my only suggestion is that you first ask eBay.