Personally speaking, drastic measures should be taken against items being vended that are actually an NPC purchase and not world drop.
Such as, items cannot be vended if they are sold from NPC.
Being said, for your case I have been told that you can contact Xealot [link] for a resolution to your trade.
I don't mind vend of potions and NPC items as long as they're fairly prices, that the main reason Merchants get their skills Discount and Overcharge for when they buy from or selling to NPC. That allows them to sell items to people at or below NPC prices, giving other players a convenience and the merchant a tiny profit. Even a little over for price is okay to me for items that are from NPC that are pain to get to like Fire Arrows to recoup travel costs. So say 4z-5z for fire arrows is okay, though I'd rather just run my merchant to the NPC and buy them in bulk myself.
But when people vend items for massively overpriced (2x or more) I have issue, specially when they use that fact that the NPC seller is not well know. There are just to many difference right now between restart and classic and renewal to be able to track them all.
But then you also run into the problem of some of the vender might not even know if a item is NPC purchasable or not. I personally have never played enough (or far along enough), even though I've played off and on since alpha/beta, to even know you could buy the basic none slotted survivor's rod till today. I didn't even know about the animal skin selling NPC till I stumbled upon them in Morroc.
edit: more spelling/grammer errors.
Edited by StarDruid, 12 September 2018 - 08:59 PM.