One of the biggest failures of society is in teaching the new generation about managing an economy. A classic example of this if found in PSO2 and the insane underpricing of everything contained in player shops.

Just as an example of this I looked up a VITA SWORD at the weapons merchant. The selling price at the weapon merchant for the sword is $5,280 meseta. The majority of these swords are selling for $2,100. Obviously people playing in PSO2 have never heard of leaving money on the table. Look that phrase up and the pricing might self correct as more people start understand the economics of the game.

Probably because Vita Swords drop like candy

NPC price varies depending on affixes and grind, so should market price, a trash weapon with good affixes that make it good fooder could sell for a lot of money.

The merchant selling a weapon does not mean people will want to buy it, you should compare at what price does the merchant buy you back the weapon.