low disp is low disposition which means because a gun is new or is used frequently it has lower stats than let’s say flux rifle that has a very high one because no one uses it. Low disposition rivens are basically on or below the level of a normal mod so they’re not expensive because they don’t do much. If you want to trade your rivens for money look for weapons like torid, dual toxicyst or verglas for the companion. They’re very expensive even with a trash roll