I think a lot of times it depends on the reason the guests claim they want their money back.
But, like CL said, keep all documentation, write everything down right after it happens, take photos if you can (if there were specific claims of 'broken this or dirty that'), have the same person deal with the guest/credit card co every time (otherwise you get a lot of, 'Well the OTHER person said...').
I have had two incidents and won both of them. I had documentation up the waazzoo. For some reason I noted every little detail with those two reservations. I don't usually do that, who has time?
I think that did it. I was prepared.