As for pricing, I look at what items have sold for recently and in the past. I look at the condition my item is in versus previous sales (I do tend only to buy stuff to sell that is in excellent to pristine condition!) and adjust the price up or down.
I tend to err on the high side if I haven't listed something before or if there is nothing else like it on Ebay currently. An example of this is the Boston Marathon jacket I currently have listed... There are no others exactly like it (at least not a few days ago when I listed it). It's something that might sit for weeks or months before garnering serious interest. But I figure that someone will search for it (it already has a watcher, so I know it's desired by someone). I set the price high and put a BINOBO on it. We shall see what happens... This also gives me a chance to test the market to find out what people WANT to pay for an item (not counting lowballers!).
As for what I paid for an item, that has no bearing whatsoever on the list price. It's all about condition and the market. The less I paid for an item and the higher I can sell it for, all the better... I recently (Tuesday) raised the prices on all my winter items because I know people will soon be looking for those sorts of things. That's the market speaking up.