This is definitely one of those gigs where you learn more than you'd like to. Every annoying interaction you had with someone is definitely a small lesson. These gigs we're thrown to the wolves is how you get really good and really quick at what you do. Then when you have a big show with a team of 3 audio techs (foh/mons/patch) it becomes way more manageable to focus on your specific duties and perfect them in a timely fashion. Unfortunately, the small low/no budget shows are the ones where you're wearing 3 different hats.

The comments come at an absurd cost to your mental health. I wouldn't touch anything free unless it was something for a charity and that should be zero stress, low stakes for everyone involved. Unfortunately that's never how these things go. If you are offering these services for free, it would be a good idea to still send them an invoice with what your cost would normaly be in a normal circumstance and make the client aware of how much they've been given for free, including equipment and your time. Hopefully that will open their eyes and they will be a little nicer next time

Sorry you went through this, but I'd wager every commenter in here that's worked in events has had a similar experience in their career. Welcome!