Because the major problem that I had with the heck-hole that I just moved my horse out of was that the barn owner thought she could tell me what to do with my horse. Always in my business, asking me what I did with my horse that day, telling me what to do with her, etc.
She was a nut job that said one thing and meant another. It didn't matter what it was about.
So one big thing that I think a barn owner must remember is that the horses there are not theirs and they can't dictate what the boarders do with them.
I think expectations must be ironed out ahead of time as far as arrangements for when boarders go out of town, holding for the farrier, etc.
And someone who is OCD and paranoid just should not board someone else's horses. You SHOULD expect that boarders respect and take care of your property. You should NOT nit-pick about every little thing.
Can you tell I just got out of a situation that made me miserable? :)