How Much Deposit for Vacation Rental?

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I have four properties that allow 30 day rentals.  Only one of them has been rented out as a vacation rental and only to family and friends and friends of friends.  It seems like some people collect a very small security deposit.  I also just noticed a VRBO person collecting a $59 property damage charge which I assume is going to some insurance company,

How do you decide what amount to charge and have you had problems when damage went over that amount?