As soon as you carry out a transaction on the network, you will be required to pay a transaction fee, also known as FEE or GAS. These network transaction fees vary according to the byte weight of the transaction, not its amount.
It is up to the issuer of a transaction to pay these fees, since the receiver is not subject to them.
Be sure to include these transaction fees when you make a sale through the Coinhouse platform.
e.g: I want to trigger a sale of €100 in ETH via the platform. The platform is asking me to send 0.575 ETH to the address: 0xcD20faC6472f9Cb1Ed3B7FCB5823d2E3f8c08FDc.
So, I have to send 0.575 + transaction fees to make sure the transaction arrives with the correct requested amount (i.e. 0.575 ETH).