My 2 cents: I was really worried about this topic recently. I bought a Kiwi Pie new for my new baby and then really needed money. I sold it on Ebay (only time I've ever done that) because I usually end up trading everything I list on the TP and, like I said, I needed real money this time.
The starting bid was $10, but the thing went for waaay more than I paid for it. I felt really guilty about that. I didn't buy it with the intention of selling it for more... it just turned out that way.
But otherwise, I never ask more than I pay, never ever sell something I got in a trade or swap, and usually trade for everything! Btw, I'm generally with Kellieblue on selling new things that don't work out: I charge the price I paid (w/o shipping) and make it ppd, so I usually lose $2 or so. But I don't see anything wrong with charging a bit more for shipping- I just figure if people have to pay the full price I paid, they'd probably rather buy their own new.