Libraries make you pay for damaging or losing books usually. I am generally of the privatized camp, where when you pay for something and it's yours you take good care of it, and if you do something to it you bear the full consequences. If you borrow, then it should be with the explicit agreement to return in original form. In fact put it in writing and have a contract made, take a picture of it. As now you are in the lending business... even if the price you are charing is $0. And if it comes back damaged and they are not willing to pay for it, or if they lose it, then don't lend to them anymore and remind them if they ever ask you as to why. Maybe you will lose friends, but then you should probably not be mixing business with pleasure.