Update: They called
I had to explain to them my reasoning behind my decision. I wasn't going to lie, knowing full well that they would watch the availability calendar.
They apologized profusely, said it would not happen again, and would I please reconsider? I told them no. What I did not mention in my first posting was that they had done this the year prior also - but only *I* saw the last minute of it, and no other guests were in the house at the time. So this was done TWICE - I have every right to deny them. Not sure if I will get a bad review out of this, but not really concerned about it either.
Thanks again for the input..