How do you deal with damage to your client's property?

Ideally, if you tell the customer, it's better than them telling you. Get pictures, measurements and try to understand the full scope of the damage. 

• Let them know what did get done according to plan
• Then what damage did occur
• Then the concession/apology. " Mr Smith, our incident rate is very low but it's not zero. It's never our intention to cause damage to your property, and can understand how you would be upset. There's a process we follow to ensure these situations are correctly and thoroughly handled..."
• Let them get the anger out. When I started, getting yelled at, off hand remarks and sarcasm all rattled my cage a bit. Now I nod as they lay it on, knowing that the steam they **bleep** off will make fixing the problem easier.
• If the anger is winding up instead of down "I'd be upset too. Maybe this afternoon isn't the best time to talk about fixing it; I'll give you a shout on Monday next week and we can discuss remediating this"
• If they want to talk about repair/replacement: the first two questions I ask are "is this something I routinely fix to a professional standard?" and "is this going to be something I want to make an insurance claim for, or try to handle myself?". As a lawn pro, our most common damage is rocks being thrown into windows. I have 2 glass firms I work with in my city that do free quote visits and usually replace glass within 2 days. The $100-500 claims are easy enough to handle on my own. 
• I run the customer through my solution process. "The odd time this does happen, we work with XYZ Glass to get the glass replaced as soon as possible. I can arrange for them to quote and fix this right away. We'll handle the cost of repairs, of course, and I'd also like to discount next month's service by 20% for the inconvenience. How does that sound?"
• Finally, after it's all done, make sure they are pleased with the conclusion. If you've done everything you can and they want more, you may want to practice this line or something like it: "As a business owner, these kinds of situations are nightmares. I am sincerely trying my best to make it right, but I can't reasonably afford to give you a 100% discount forever, or replace all of the glass on one side of your house. I've done everything I can to ensure we're looking after you, but the message I'm receiving from your side is that it simply isn't enough. At this point, I'm going to have to defer this to my insurance as a claim. I'm sorry we couldn't work this out, and I understand if you do not want to continue with our services at this point. Perhaps I can point you in the direction of other service providers with strong reputations in this area to continue for you."

Tone is everything. You may be freaking out a bit about the cost, extent or source of the damage. If you approach the problem confidently but not cocky, you'll inspire the same response for your staff and the customer. It's not just about doing what's right, but that is important too. I have found that a customer that didn't love their window broken might still be impressed with the way the problem was handled. Navigating a difficult situation like a pro can increase their loyalty to you. If you sweep it under the rug, or decide that now's a good time to be stingy with their repairs - you may find yourself on the receiving end of the dreaded 1-star Google review. It's probably less expensive in the long run to be thorough. 

Also, **bleep** happens. You're going to be fine.