NPC Fetching.
Only one problem I see.

They don't tell you how much they'll pay for X thing.

So you never know if buying it for Y is going to gain or lose you money.

I think maybe they should say something like, "I'm looking for a watchamacalit and I'll pay X chyen for it."

That way you know when a bargain is good, and when it's bad. Because realistically if I buy X thing and then go to sell it and a guy offers me half, I won't sell it, but you don't have that option in this game, it's just a leap of faith as to what they pay you now.

Or think outside the box! Could be dangerous.

Stats can have some effect on what the NPC buyer will pay for the order, too, but unless you're DEEPLY committed to making this mechanic a MAJOR focus of your gameplay, this entire scenario is a really bad way to grind out your income anyway.

For a lot of reasons, some mechanical, some not.

This isn't a farming game and for many people much of the time, this deal isn't very advantageous unless you're already getting the loot for next to nothing. And that's not EVEN because of whether or not there's a risk that the NPC will underpay

Anyone who has read the topic on the weekly income cap should understand this.

The magic WIN button isn't the one marked "ask NPC if they need anything today". It's the one marked "roleplay with human beings".