This is what most "story content produicers" will try to sell you
http://www.1stsexstories.com
Scroll down untill you see the red lettering, theres no popups...
Its like 3k stories, they were first collected from usenet groups by underworldcontent.com and given away for free.
If you have bought any stories from anyone, check out the titles in here and then see if any of them match, if they do, then you know you bought content they dont own.