Most trades I have done (I am new so the number is not real big) have been audio CDs. I have never asked anybody to just send FLACs and I have only been asked to do it that way one time. But what I do when trade discs come in is extract the waves with EAC, convert them to FLACs, then archive the FLACs on DVD. If I were just being sent FLACs it would save a step for me, but I suppose not everybody uses a similar system.