Gold trading ...

Here's my understanding of what happens. In what follows I'm quoting prices WITHOUT the admin fee unless I say otherwise.

First one person makes an offer to trade (either to buy or sell gold for coins). That person gets charged an admin fee of 2% of what they are offering at that time. Since we are assuming this is the first half of the trade I'm also assuming that there is no matching trade currently offered and that the offer gets added to the list of open offers.

When the offer gets accepted the accepting party pays both the asking price AND an additional 2% admin fee on top. It only affect who has what between the offer being made and the second party accepting it.

The order in which things happens (wether the original offer is to buy gold or to sell it) makes no difference to the ultimate outcome.

As and example if you BUY gold for 392K and sell for 408K you actually pay 399.84K per unit and receive 400K per unit.

The 399.84K purchase cost is made up of the 392K plus an admin fee of 7.84K.

The 400K sale receipts is obtained by dividing the 408K received by 1.02 (the number of units of gold you loose from your inventory when you sell 1 gold and pay a 2 silver admin fee).

The net effect of the two above trades is a profit of 160 coins per unit of gold traded.

Additionally you need to sell at above 104.04% of the purchase price to cover both purchase AND sale admin fees.