Never satisfied tenant, how do i handle this.

[Gary Dale McKee]

I have a tenant who suddenly finds something wrong at or around the time of their monthly payment.  This has been the case so far every month of their lease.  I have fixed these minor issues within a day of them telling me about them every time.  I am beginning to believe this is on purpose and their way of making life a little less easy for me.  I am really new to the business and have bent over backwards to make these people happy and it seems that isn't possible.  What do I do?