20% for things the traders don't want is reasonable.
Sometimes people are just in a hurry to keep playing and don't care about optimal logistics.
A player could just scavenge and explore across the world, getting what they can as they go along.
Like an RP mode where getting ripped off is just part of "Wasteland Harsh".
As for Wasteland Harsh, no drop should end at Lv24, when the "Real Game" starts.
In this case lv1-23 would also be a sort of "tutorial".