Do you rough board? The first barn I boarded at had a BO that could care less about the maintainance of the property and we had to do everything ourselves. So I would grab my hammer or buy an occasional new board and all of the boarders chipped in when the water pump broke. If you buy the shavings why the heck can't you keep your stall as you would like? But If you are on full board than I believe you would have a right to ask for a clean stall and a suitable turnout situation.
While I plan on taking on the venture of owning a small boarding facility myself, I have thought alot about the conditions I am responsible for providing for other people's horses too. It doesn't have to be a fancy la ti da place, but it should offer sanitary, safe conditions that a horse is noticeable happy in. I pass so many barns where the horses are standing in small paddocks filled with six inches of mud and manure, covered in flies and surrounded by broken boards and they look positively miserable. Yeah, they may get water and food, and technically you wouldn't be able to catergorize their conditions as "abuse" but it is - to me it's psychological abuse - something the SPCA doesn't really focus on.
I know that if I do take on the responsibility of becoming a BO - I would feel responsible for every scratch, rash or mishap that would happen to anyone's horse while on my property. And you bet if one of those horses were sick I would monitor it as if it was my own mare. The barn I board at now often tells me about scratches that I hadn't even noticed on my girl yet. They also give me updates on how whether Fri seems "off" today, if she's in season, or anything funny or cute she did for the week. I like these updates because it tells me they really care and are watching, which is really one of the most important things I pay them for.
Just be careful.