I keep it simple - unless it's someone I know well personally (and in that case, they've probably already had a go on whatever I'm selling), there are no test rides. All there is to it.
Money in hand, or not - until the title is transferred over to them, liability is entirely on you (the owner). And few have insurance coverage for 3rd party operation of their motos (while common for cars, in that it's substantially lower risk).
I don't care if the buyer even has a driver's license, or motorcycle endorsement. I don't care if they're legally in the US or not. When I have their money and the title is signed over - they can do whatever they want with the bike.