Great question. I have sold a number of motorcycles and only one person asked to ride first. The bike had full coverage, the kid had a valid motorcycle license and guaranteed me he'd pay for it if he went down (yes, I asked). All went well, but I was second guessing myself the whole time he was gone. I knew he wasn't going to take it since I had his truck that was probably worth more.
If it were to happen again, I would make sure they had a valid motorcycle license (as before) but would also make a call to my insurance carrier. If your insurance would not cover it, I would ask for their proof of insurance and would consider calling their company myself. Anybody seriously interested wouldn't mind the extra hoop. How's that 'ol saying go, "an ounce of prevention"...