If a guest doesn't seem appropriate for your listing or unmanageable for you, you are free to decline them with no penalty. Just make sure that when you are completing the decline drop down screen, you uncheck the box that wants to automatically block the dates that the declined guest was proposing.
The late discovery that your calendar has been unnecessarily blocked all week is a self inflicted penalty in and of itself.
Cancelling a reservation is where you start to earn penalties.