My friend and I played in bands back in the 1960s/70s but don't gig anymore. Now we do sound for mostly bar bands, and some fairly large outdoor shows. Sometimes we do open mic nights where we have no idea if there will be a fiddle, accordion, and a flugelhorn show up and join the guitars, and maybe a pedal steel player on stage, with a doghouse bass and four, or five vocal mics all at the same time. We get complimented by bands and audience members on what we do, so I think we must be doing most things well.
I find guitar players to be the hardest to deal with, mainly because of stage volume, and also the over-use of pedals that make their guitars sound very bad, and with drastic level changes as they switch things in and out. Whenever I see a giant pedal-board, I expect that our job will be more difficult than I would like. When necessary we ask guitarists to turn down. Most do initially, but then as the night progresses, they turn back up. We often end up with their channel turned all the way off in FOH, and get requests from the audience, (often musicians themselves) to turn down the piercing over-distorted guitar, (in a modern country song where it seems inappropriate to have such a distorted sound). We once had a pedal steel player crank up a Fender Super Reverb into crunchy ear-spitting nastiness, (on a pedal steel yet!), and he said that is the only way to get "his sound". Ruined the jam for everyone else on stage. You should have seen the other people on stage staring at this idiot.
When this stuff happens, we just tell people in the house, "Sorry, there is nothing we can do. He's not even in the FOH".
About 25% of the drummers love to hit hard, and we usually just say something to them like "Hey this is a small room, so try to take it easy on the volume" That helps sometimes, but often our recordings are filled with drums in the vocal mic channels.
I find that bands who go amp-less, and in-ear to be the easiest to work with to get great live sound, and live recordings.
I like to DI (pre) as much as I can to give us a chance to have a signal that we can make the best use of, but if the guitar player cranks his 100 Watt Marshall at a venue where I could get by with a 15 Watt combo, (miced, if needed), I just accept the fact it is out of my control.
We have had almost no problems with bass players.
I would never adjust anyone's amp, (unless they came to me and asked for help), which has happened a couple times.
The bottom line for me, is we do what we can without trying to tell someone how to use their own gear. If they have crappy tone, I just assume we have a difference of opinion of what sounds good.
We try to accommodate every player as best we can. We use good equipment, and our schedule is full, so we must be doing something right. I have a policy to never say anything negative about any performance or tone to my partner at these shows until after we have loaded out and are on the drive home. The easier people to work with are also the ones that pay the best.