@Deanne35 we charge damages if the item in question costs over $50 to repair OR its a piece of furniture that obviously needs replacing to complete the decor of the space (like a kitchen chair for example.) We don't charge for missing towels, broken glasses or minor stuff.
Like you, we had someone damage our slate on the porch. Tried power washing and any number of cleaning remedies but ended up covering it with a cute rug. It was too expensive to replace the whole thing. Ironically, that is something we really should have charged the guest a hefty fee for, but the difficulty of doing the work during COVID in time for our next reservations gave them a pass. They got charged for the rug instead.