Buying used PC: Does it have a good product key

I'm about to buy a used PC (via Craig's List) from someone I do not know, with Windows 7 installed. It's an older machine, and there is no Microsoft sticker on the back. Using My Computer > System Properties, the Win 7 Basic Information page says "Windows is activated" and has the little "ask for genuine Microsoft software" icon on the right side of the display. *Should I have any concerns?*