one of the best things you can do with bands is provide a plain-english mixing agreement for them to sign. it won't hold up in court, but this is for bands that can't afford what you're worth let alone what a lawsuit would cost anyway.
i make it really simple. 50% down in case of band disasters and nothing more than a 128kbps mp3's until payment is made in full.
here's the crucial part: they get the first mix from me and they listen to it. i get ONE list of mix changes from ONE predetermined contact person (noted on the agreement). i then make those changes and await a FINAL SET of tweaks. these tweak must be found by me to be just that, TWEAKS not changes that require i remix the whole song. if I AGREE to make the final tweaks, then that's what they are, FINAL TWEAKS. if the band decides they still don't like what they have (after three mixes i've done that they can now choose from), it's over. they pay me in full to mix it again or they take their ball and go home. at that point, i truly don't care either way. they chose me because they generally like what i do. if they don't like my take on it, there are lots of other chefs out there to make their soup "better".
with those rules spelled out, i can always go back to the agreement when things get nutty. they often do.