I agree with Red. You really never know what is going to happen whether your selling or bidding. I personally have had items with a bid of around $50 in the last fifteen minutes of the auction shoot up to $300 by auction's close. I have also had items sell for a fraction of the EBay average for like items. You also have to take into consideration the quality of the item. A cherry A4000 will typically go higher than one that is damaged or status unknown. I would like to think that price is heavily influenced by accurate pictures, proper description and seller's integrity....the jury is still out on this one though.
One thing that really annoys me is sellers who list a used item and use a corporate image of the item in new condition. There are these great pictures of this brand spanking new item and the description reads something like this "LQQK - Widget IV - The Ultimate in Widget Technology! - Don't be fooled by imitations - This is the Real Deal! - Upgrade your Widget to a sleek new Widget IV....etc." Then a little lower you read "This auction is for an untested used Widget IV - As Is" Then I see that item sell for retail price. I would not miss these types of sellers at all.
When I am selling I want to get a good price but not at the expense of misleading someone. When I am buying I want to get a good price but I am willing to pay a fair price if everything looks good such as pictures, description and seller's rating.
When bidding, remember that there is usually another one around the corner and never bid more than you are comfortable with. If you are making a planned purchase , I would recommend performing a completed auctions search for the item you intend to buy. Find out the average price and use this amount as your initial price ceiling. Then adjust this price depending on factors such as item's quality, seller's rating, S/H charges etc.
Dave