one easy rule to weed out the merchfood
The shields Req plus 8 should be it's armor value
Q0 = 8 Armor shield is max
Q5 = 13 AR
Q7 = 15 AR
Q8 = 16 AR etc
Below q3 won't drop in gold.
The ones i listed above 5/13, 7/15, 8/16 are wanted in tactics for pvp.
8/16 command is kinda wanted.
Moti/strength not so much.
But any req + 8 = its armor shield can be worth selling if gold, and even purple and blues can have a little value sometimes.
Popularity of the skin / rarity sets the value.
That one q0 ar8 insc blue kournan defender got a lot of attention because only kournan military drop the skin, and it's not easy to find the kournan military of the proper level to get one to drop.
(Only a few foes during one early NF primary quest).