There are several other threads on here covering this topic. It's a personal choice. In my case, I subscribe to the theory that " you break it, you buy it". If I borrow something from someone I give it back to them clean, full of gas, and in the same condition that I borrowed it in. I expect the same from anyone who borrows my stuff. Treat it with respect, fix it if you break it and you'll get to use it again. Don't and you won't. It's pretty simple really.
Make sure to tell people up front. For example, my wife's cousin is coming in from Washington to borrow our cabin this weekend. He and his wife have never snowmobiled before so they don't know what to expect. I sent him an email outlining some of the costs of snowmobiling, i.e., what a gallon of oil costs, what gas we use, cost of A-arms, bumpers, windshields, etc., the common stuff. Then I told him how many of these things we broke last year so he knows what our experience has been recently. Now he knows what I expect. Hopefully this will avoid any misunderstandings should he break something.