You need an auction house to start with. When upgraded, this generates silver-ish coins you can use for the auction.
The line in the table falls green when you have the highest bid, red when your bid is not the highest [and blue when you are the seller].
In the end the winner pays the price of the number 2 bidder +1.
fi
i want a player and bid 100
you bid 250.
You win and pay 101.