Market takers are responsible for covering the gas fees associated with each trade. Given our design, the exchange must pay this gas fee, priced in ether, when dispatching the trade to the network and then deduct it from the balance of the market taker. When exchanging tokens for ether the amount of eth deducted matches that of the gas fee. When exchanging ether for tokens, IDEX deducts the equivalent amount of tokens based on the price of the asset in ETH. This price is calculated using the average of the last 10 trades.
Ethereum gas prices have been increasing and often this fee is higher than the IDEX exchange fee of 0.2%. These high gas prices have led us to instituting order minimums in an attempt to reduce costs for our users (see question below on trade minimums).