to see what the average going price for your item is when you sell it.
However, there are alot of factors on ebay. Like i just bought a DVD player for $26. Three weeks ago, there were some new DVD players going for $10 and no one took them, now you can't get a broken one without $50. Demand can fluctuate.
You might want to talk to addickt to, i know he, among others on this board, has bought & sold shit on ebay habitually.
I love EBAY. Been on it for over 3 years and have bought and sold damn near 1000 items with little or no problems. You name it and someone is selling it.