All this talk about who's entitled to what money and such can be pretty confusing, so I thought I'd write up a (half-facetious, half-serious) Gemshop Bill of Rights.
 

Apu's Gem Shop Bill of Rights

 

1. The Trader has the right to charge any amount of money for selling the customer's pouch (including zero).
   
    
2. The Trader has the right to charge this fee without informing the customer (known as skimming) - as long as the Trader does not actually sell the gems without making sure the customer is satisfied with the price being offered.
   
    
3. The Customer has the right to turn down a Trader's offer for their gem pouch - the customer then has the right to decide to sell the gems himself, or find another Trader to sell them, or throw them away, or whatever.
   
    
4. The Customer has the right to be dissatisfied with their dealings with a particular Trader, and to avoid doing business with that Trader in the future.
   
    
5. a) Apu has the right to scroll the hell out of everyone in the room in an attempt to optimize his gem pouches and learn an extra .0001% trading skill.
   b) Everyone has the right to squelch Apu's annoying scroll and/or thump him for being annoying.
   
    
6. All your gems are belong to Apu.

So there you go, now you know who is entitled to what. It actually turns out that the 'extra money' that a Trader might earn the Customer isn't 'entitled' to anyone in particular. In fact, the Customer is entitled to demand that the Trader pay him any amount he wants for his gems; the Trader is entitled to offer the Customer any amount he wants to give for the gems; and both parties are entitled to cancel the transaction at any time if they don't like the demands of the other party.

And if that is too confusing, please refer to #6 on the Bill of Rights, and turn over your gems to Apu, he's too busy chasing circles to worry about charging little fees or worrying about who should've been entitled to all that extra money from his bonus. Well, that and I make more in tips offered freely than I'd ever make from charging fees or skimming.

Apu