Let's say your character level is lv59.
You equip your character with -1 lvl requirement hat, armor, pants, accessory x 2.
So total -lvl requirement is -5
Right now, any weapon or equipment will be shown to you as -5, meaning a lv58 sin saber will now show you as lv53 required to hold.
Thus, a lv59 character with -5 lvl requirement equipments is able to hold a lv64 weapon which has higher damage than a lv58 weapon
So for those who manage to find lobangs for -lvl requirement, it is still good to invest some gold on it for future purpose.
Some guidelines for the pricing:
Hat -1 lvl = 80g and below
Armor -1 lvl = 10g and below
Pants -1 lvl = 99g and below
Accesory -1 lvl = 100~150g
Hat -2 lvl = 180~200g
Armor -2 lvl = 180~200g
Pants -2 lvl = 200~299g
Accessory -2 lvl = price unknown
Hat -3 lvl = price unknown
Armor -3 lvl = price unknown
Pants -3 lvl = price unknown
Accessory -3 lvl = dont know if it exist