Luckily I get to mix the majority of the projects that I track, but if that is not the case i want the session to be organized, intuitively laid out with a track sheet and notes. If its in a DAW, edit points cleaned up, and unwanted audio removed so as not to cause confusion. Labelling should be clear , not some esoteric explanation.
I do not have a preference as long as the music is good and the people are nice and respectful , even fun.
For mix considerations, I do listen to a CD of the songs to see if I think I am the right person.
I like the mix sessions to be delivered as organized, detailed so that I can mix and not have to clean up somebody else's sloppy work. I am hired to mix and anything that saps my energy and creativity away from that task is annoying as hell. Plus its a diservice to the artist.
But I understand how it happens, I just care not to deal with it.
tutt