Striving for fairness

I know, due to deadlines, that this isn't always possible.  Still, if I were a newspaper critic, I'd want to see at least two nights of any performance that runs more than one night.  I realize performers are supposed to be professionals and always do their best, but life sometimes gets in the way.  The air conditioning at a venue might not work one night.  One of the leading players might feel somewhat under the weather.  The audience might be unusually picky on another night and not applaud too easily, leading to a more subdued performance on stage.  Many variables can affect a performance, and as a reviewer, I'd want to make sure I'm being as fair and objective as possible.