transyo23,124 09 Sep 2017 09 Sep 2017
Once you unlock the trader, simply sell everything you don't need. All weapons that you aren't using, all armour, shields, items that don't have any benefits. I find it beneficial just to keep five of each thing - and keep the top ranked items for those five.
Sell each time you go through the dungeon, and you'll unlock this in no time.