You might decide to put aside the indignation and man-up to some shortcomings on the day. The deficit of airmanship and etiquette might be partly explained by inexperience and unfamiliarity; one constructive approach might be to put this on the record and request a more comprehensive briefing and/or check. In effect, you could start thinking more like an owner and less like a renter. This would also give you the opportunity to demonstrate and see if you can reproduce the radio issues, and to clarify whether it's a real technical issue or finger trouble.
I've rented and owned many aircraft and, when renting, have always tried to go the extra distance in operating and returning the aircraft. Similarly, when others have rented my aircraft, I've left them in no doubt from the beginning what my (high) expectations are. People come from many different training and life backgrounds and a good first briefing is important. In your case, the group rep might have recognized that your briefing was not perfect and offered you another or you could, as I've suggested, have asked for a second one.
At the end of it all though, there is no excuse for leaving the aircraft in less than the best possible state. You've explained some mitigating circumstances but part of being a pilot is to learn to put all those aside and do the right thing by the aircraft, owners and subsequent pilots. Operating aircraft in hostile conditions with sometimes needy passengers does help clarify what your priorities as PIC should be. Chalk it up to experience.
I wish you luck in resolving the situation, and rest assured that being a good group member will stand you in good stead as a future owner.