I tend to use the default price as the price when I sell something on the Marketplace, and I assumed it was either the lowest price among the items offered, or an average of the prices.
But when I checked the prices by searching in the Marketplace, I've found that often the prices don't tally. Usually, the Marketplace price (not the autodisplay one in your Inventory) is much lower.
Anyone know why this is the case? I don't know how the autodisplay one works, (as in, how it calculates the value of your items) but I do know that it's often wrong...