To be accurate: placing an order costs a fee, canceling an order costs a SECOND fee.
This is even worse than I feared. First of all I placed a small order to test, which I cannot cancel anymore because the fee is larger than the trade amount.
Second, if there is a fee for cancelling orders and placing new ones at a a different price for example, that makes the whole decentralized exchange idea uninteresting to me. How do you expect someone to start an arbitrage bot and to support the market peg, if cancelling or changing orders costs money. I for myself go back to traditional exchanges.