Lots of good points. I'll add a few that I didn't see mentioned yet.
1) Get your agreements with your clients clear and in writing. Signed. Dated. Both parties. Period.
I got bitten in the ass by enough "I don't need a producer" artists to learn this the hard way. It sucks to suddenly have the expectations of your performance suddenly and bizarrely altered after the fact and NOT have something in writing to help restore level-headedness.
True story. I travel 6 hours to a remote singer/songwriters place to start recording his album. The plan was to teach him and his partner to use their mBox and set up their room, record 1 or 2 songs to try and finish, and establish a plan for collaborating via the internet so I can add parts and mix at my full rig back home. For this they have budgeted "2 Days."
Now you and I know that "2 days" in the studio can be anywhere from 10 hours to 30 hours. Since we were all dedicating these days to the project I figured on 12 hours a day and told them so. They agreed.
After the evening setup (not part of the 2 days, also discussed beforehand) and starting early on day one, we had burned through about 10 hours by break time mid afternoon and gotten most of one song done. When I brought up how much time had passed the guy turned white. "Oh," he said, "we only budgeted for two 8 hours days. We don't have enough time left to accomplish what you said we could."
Grrrrrr.....! So I reminded him of our conversations earlier. He said he thought I was telling him how much I was WILLING to work not how much time would be billed. So I said we could switch to a block rate (which he had refused earlier for some reason) and work the balance of the 2 days at about the same amount he had budgeted. We agreed.
Without having to watch the clock his performances sky rocketed. He insisted that we switch our plans to recording vocal and guitar takes of ALL his songs to use as templates for the rest of the record. Um, ok. I used it as an opportunity to get his wife all practiced up running the PT rig so they could continue working after I was gone (as originally planned.)
I warned him that we were working too fast to achieve much quality. He didn't even want to listen to a take after he had decided he got one with a good feeling. I said about 9 times that he was going to be dissapointed by the quailty when he listened back, but he insisted he had the right feeling and that was all that mattered for the other musicians to get their parts right. He'd redo the guitar and vocals when he had more time and the rest of the parts to do it with. If we stopped to listen now he'd lose his groove. Fine.
We finished all his tracks, I transfered the sessions to his computer made sure they knew enough about what to do with Pro Tools to start off on their own (and even that, they agreed, was almost more than they could absorb), packed up my stuff, collected my check and drove 6 hours home fairly satisfied with the work accomplished and the project ahead.
Next I heard from them was 2 months later. I got a long, nasty email about how bad it sounded, how unprofessional I was, and how they didn't know how to use pro tools, I was a bad teacher and they didn't have the 2 finished songs I promised. (sigh.) I wrote a long *very* clear letter back describing the events as they occurred, the agreed shift of gears, the warnings of low quality, etc. Throughout I asked what I could have done to be more professioinal and at the end offered them some money back if they still felt I had not performed as expected.
I got an apologetic letter in return. "Sorry, I was just frustrated that my project has taken longer than I thought it would and doesn't sound like I want it to. I felt that way with the last 3 engineers, too. Its not your fault, I just don't know if I want to finish the project. You did fine, I just thought it would be quick and easy."
So, yeah. Get it in writing BEFOREHAND if you can. At least this couple was brave and honest enough to communicate clearly with me instead of just going off and not letting me know what was going on.
2) Don't send working mixes home. Ever.
Trust me, the girlfriend isn't going to understand what a "WORKING Mix" is and the guitarist is just going to come back mad the next day. He won't say "Man, my girlfriend doesn't understand this process and thinks I'm wasting my money! Ha ha!" and he won't tell you he's having doubts about your skill. He's just going to up the pressure on you to make is sound more _______! (Insert ridiculous phrase). Then you'll be wasting your time trying to make it sound like its done when it isn't. And they still won't be happy unless you mash it through a compressor to make it loud like thier other CD's.
Or, worse, they'll just assume you're just an ignorant asshole trying to scam them and never come back. And loudly boast to all their friends how they caught on to you quick and left without paying.
All because you wanted to be helpful and sent a working mix home and the girlfriend didn't think it sounded "professional." It doesn't matter how much you warn them, they'll still start to lose faith in you.
Good luck!
Chris