There are a lot of great points here. I am currently in a situation that is similar. Apologies for length.
The barn where I boarded for 10+ years sold at the end of 2020 so I had to find a place to board my horse while waiting for my barn to finalize (which will be the end of this month!). In the interim, I reached out to a horse friend of mine that I have known for several years (we actually met when we both boarded at my old barn, back when it was not private) who has a very small, private farm with home on-site that is close to my old barn. I am currently the only boarder so it is my horse and her four horses at a six-stall barn with sufficient turnout.
My friend charges more in board than I was paying before so I asked her about ways to work off some of the cost. We found that my shift schedule as a nurse would allow her to go on some vacations and work trips as she has always complained about never finding knowledgeable and/or reliable help who can cover the barn for 2-4 days let alone anything longer. We discussed this possibility and I was upfront with her about how my work schedule has set weekends (Saturday and Sunday) and holidays and I do not always get the requests that I make, as well as the fact that I have my own competition and training plans for myself and my horse. I also commute 30 minutes one-way to the barn.
She has always had her barn set up as an LLC and has had multiple boarders of the 5+ years that she has owned the barn, so the board contract was more of a legal, business agreement and less of a friendly contract. I signed the contract (and waivers, etc.) for full/total care board and she stated that she would pay me directly (cash, check) for any work that I did; this way I did not feel bound to anything, plus CYA. She has a history of going scorched earth on anything.
Largely due to the factors that I had discussed with her, I was never able to cover the barn for her. The first time I was lined up to do so was a few months into being there, I had a family emergency which required me to go out of town on the dates that I was supposed to barn-sit. I told her about the situation immediately, which was two weeks before the dates I was responsible for, and already had three horse friends lined up to help me. Nevertheless, she freaked out and it made things very tense between the two of us for several weeks. I was so upset by how she acted during that time, especially given the gravity of my family emergency, that I never wanted to help her again. I inquired about other boarding facilities but nothing really met my criteria so I decided to tough it out as I had already told myself that this was a temporary situation. I told myself that the most important thing is that my horse is taken care of, the rest I can deal with over the next few months. Ever since that incident, I have met her energy and started to remind her that I am paying her and we have a contact so she better keep her end of the bargain. For example, she goes through phases where she does not ride for several weeks to months due to her many and demanding professional/career pursuits. Therefore the arenas do not get drug consistently and I have to ask her to do it, which always feels like stepping on a mine field because I feel as if I never know if what I am about to ask or say will send her into a fit.
Though she and I agree on a basic level about the care and management of horses as well as training, we have very different goals with our horses. We also have vastly different personalities. I have always been a great boarder, my horse is lovely and low-maintenance, and I am respectful of her and her husband’s privacy since their home is 500 feet from the barn. The more time that I have spent with her, the less I like her. I cannot wait to leave in the next month. This experience has made me extremely wary of sharing with others when I get settled into my own place.