In one of my rentals I have a tenant who's often picky about minor issues. The tenant is mostly a good tenant and I make an effort to fix major issues quickly. However the tenant will often bring up minor issues or issues beyond my control, almost one a month.
Here's an example. The master bathroom shower handle broke and the shower was unusable for a short period of time due to my normal plumber being unable to fix it. I found a plumber who fixed it. About a month later, the tenant complained that there's a slow drip from the shower every 3 seconds and his wife was having trouble sleeping because of it.
A fix to a shower can end up being a major repair, especially if the wall needs to be ripped open to replace the valve. I'd rather not touch it because it's working perfectly well otherwise.
There have been other issues which I've sometimes fixed. As a landlord, where is your "line" between essential maintenance and the tenant being unreasonable?