On my web site I have my rules for ebay, Ill repost them here:
-- Taken from http//internet4x4.com
Ok so you want to Ebay, here are a few guidelines I use:
#1: If the item is brand new and you can buy it locally, never pay more then
50% of retail for it, including the shipping. Why spend more for an item you
can't usually return?
#2: If the item is used and you can buy it locally new, never pay more then
25% of retail for it, including the shipping.
#3: Item can't be gotten else where? Set a limit and stick to it. I have
watched people pay $100 for a $5 item. Just because its for sale does not
mean you have to buy it or that you have to buy that one.
#4: Collectibles, only buy if you know 100% what it is you are buying and
the vendor has extremly good feedback.