A trader pays you 0.2x an item's value and sells it back at 3x, so anything you buy to flip loses fourteen fifteenths of its price on the way back through the door. Quest tier is the only real discount: 5% off per tier, to 30% at tier 6. Quality moves the buy price between 1x and 2x on top of that.

831 of the game's 1,413 items carry an economic value, and only those can be bought or sold; the rest have no price at all. Ten inventory profiles decide who stocks what, so which trader you walk to changes the list rather than the price.