For eBay, I rarely post auctions, maybe 2-3 a year. I typically do buy it now listings with NO best offer. I don't want to give buyers any leverage or inkling that my price is negotiable. If people do email me for a slight discount, I review it on a case by case basis - heavily impacted by the potential shipping cost.

Listing duration varies so much. I often aim a bit high on price for rare items, so I can often wait 4-8 months for some to move. There are certain items that I know are popular and almost always move in a few days or weeks. It's usually a function of how much demand there is and the price point. I never care about listing duration since almost all of my listings are free with my store, and simply patiently put more hooks out for the fish to bite at -- whether that takes a day, week, month or year. This may be unique to me because I have no costs to recover from the free recycled items I find.

However, if something is really stuck with no watchers, I'll assume that my price is too high and will lower it in small increments until I get nibbles. If that doesn't work, I may part the item out and sell it in pieces, or take the listing down and donate it.