How to check articles are not spun?

I am to order articles from several sources, and looking to book 1000+ articles, but I want to make sure they are not just spin off and spun articles of original content. How do I assure that? I want 100% unique content, but I need to make sure it is actually that so I know if I am getting cheated or not.

I don't think there will be any way to be 100% sure of original content, especially with such a bulk of articles, but running them through a copyscape account could at least give you a good indication of possible dupes.