Market takers are responsible for covering the gas fees associated with each trade. Given our design, the User must pay this gas fee himself/herself priced in Ether, when dispatching the trade to the network. When exchanging tokens for Ether the amount of Eth deducted matches that of the gas fee.
Ethereum gas prices have been increasing and often this fee is higher than the Blockonix exchange fee of 0.1%. For the current fee, you can check https://ethgasstation.info/.