I'm not opposed to adding something to the posting guidelines, but there's an issue here.
When I mix, I use some two buss processing, usually a parallel compressor, a tape simulator, possibly a M/S processing plug, and a limiter.
When I print the mix for the band/client, I give them a version that's not squished, but is in the ballpark of their other commercial CDs. I do this because if I don't, the band invariably wants to tweak the mix forever, since it doesn't 'sound right' to them. I also find that mixing into a limiter changes some balance decisions a bit. Things like the kick and snare can be a bit louder if the mix is limited, and still sound right.
Now, when I send the mix to a mastering engineer, I'll take my limiter off, and and possible some other 2 buss stuff, if I feel my plugs aren't a clean sounding as I want. I also lower the output level a few Dbs, since without a limiter, the possibility of clipping goes up.
The Mastering engineer gets my 24 bit, unlimited, lower output file, as well as the 16 bit limited reference file. That way he can hear what the band is hearing, and hopefully get the same vibe, but better.
I don't get complaints from mastering engineers, so I guess it works for them. The sessions I've attended have always gone smoothly.
I'd say that people should be careful about over-processing a mix that they're giving to the band (talking 2 buss processing here) but be aware that a totally unprocessed mix is going to sound a little weird, quiet, and the band may have a hard time getting past that to hear the actual balance, effects, etc.
I don't think we need to go too crazy with rules yet, things are still developing.
Just be aware that if a band sends out tracks to two or three mix engineers to decide who should do a project, there's a good chance that the other guy(s) are limiting the 2 buss, and the band may not be able to get past your low-output, overly dynamic mix (even if it does really sound better, and would be great once mastered!)
I think you need to give them as realistic a view of what the final product will sound like as possible. That's just my philosophy, though!