I learned from a very wise innkeeper a long time ago, is it worth the hassle and stress? If you can say YES, then stick to your guns.
I had a terrible week two weeks ago with last minute cancellations and no shows and nobody wanted to pay. (They were third party bookings, a DR through an agency, a guest of our local college and then the couple who called from another state at 4pm). I was determined if it was the last thing I ever did, to get the $ from those people, which I did successfully. But it took much effort. I was not going to let them walk all over me.
But I have had people pull stunts last minute that I was already frazzled and just let it ride away. Saved ME a lot in the end. I wanted it over with and out of my hair..