I plan on selling something today, I can't decide whether to have it up for auction or 'buyitnow'. Also if auction, how long should I make the bidding (2 days? A week?)? Any additional advice would be appreciated.
If you know more or less what an item will sell for you should use the Buy It Now option to get a quick sale or at least put a minimum reserve on it. For collectible items or items you don't really know the value of you should let them ride on an auction; one man's junk is another man's treasure.
For an item that has a narrow market (not many potential buyers) you should put it on a 10 day auction to maximize it's visibility - you'll get more bidders in a 10 day auction than a 3 day auction.
But for common items people don't want to wait for an age when they can buy it elsewhere right now; a 5 day auction is better for common stuff.
Maybe not the best time to be listing an auction (5 or 10 day) as so close to Christmas; either people won't bid on it as they know it will not get there before Christmas, people are all spent out now, and there are usually postal delays/items lost at this time of year also