You did not get the point.
If you own a Galaxy S and are trying for a quick sale. You won't make over 16-16.5k or so.
However, if you are a buyer and want a Galaxy S quickly, you are literally forcing a seller to go against his wishes as he doesn't have any intention to sell and will sell only at a premium. In that case you will need to shell out around 22k or so.
Mark price always has two prices around which it fluctuates. A buyer's price and a seller's price, sometimes the difference in huge and your desperation and efforts form a significant part of the price.