Ethos Trade currently charges 0.3% when you buy and 0.3% when you sell. The exact fee always shows in the Fees row of the preview before you confirm a trade.
How the fee works
Buying: the fee is taken from the WHUF you spend.
Selling: the fee is taken from the WHUF you receive.
Fees are burned. They don't go to Ethos or to the person who created the market.
Other costs
Gas: every trade is a transaction on Base, paid in ETH from your Ethos wallet. It's usually very cheap.
Creating a market: costs 5 WHUF, which you don't get back. See How to create a market on Ethos Trade.
Do market creators earn fees?
No. In the old ETH markets, creators earned a share of every buy. On Ethos Trade they don't earn anything from trades in their market.
Fees can change over time. The preview always shows the fee that applies to your trade.