G.A. Mavon Insurance states on their website

Insurance Your Garage Needs

As the owner of a professional garage, you understand that when customers hand you the keys to their car, they are giving you access to their investment of thousands of dollars. Make sure that when you have clients’ vehicles in your care that you are not just keeping them protected — you are keeping yourself protected too.

An Add-On That Can Save You

Although you have insurance for your business, separate garage insurance can be an added policy to ensure the safekeeping of your customers’ cars. Sure, your tools and industrial-sized box are covered in case of damage or theft, but what happens if one of your mechanics accidentally smashes someone’s window with an errant hammer? Accidents happen, which is the number one reason that separate garage insurance is such a smart idea. G.A. Mavon Insurance states on their website that there is a limit to how many vehicles are covered under these policies, so if you run a very large garage be sure you know what these numbers are.
Responsibility for your customers’ cars is what keeps your business afloat. Nobody ever intends to damage anyone else’s property, but in your busy garage with so many hands you want the protection just in case. A lawsuit is not worth losing your business over.