product key

Hi, I have been selling software on ebay for a long time but never sold Microsoft sw, does anyone know where the product keys that many sellers sell on ebay come from? what is the origin? I think there are 2 possibilities but none of the 2 mi convience 100% maybe these sellers generate keys...

My laptop is running Win 8.1 which was installed by the guy at the store ,so I'm guessing its pirated. I've been getting popup messages to 'Activate Windows' . Since I don't have the product key I ca't do it. I found out I can use activators to generate keys. Is this safe? I just want to...