Not sure what you mean. Since they're articles written for you, are you wanting to check whether the writer has taken someone else's material? Are you wanting to clarify who holds the copyright to the articles? Something else?

Your best defense is to know your writer and his reputation. Better yet, do the writing yourself.

I use plagiarism finder. All you have to do is copy the text you want to check and paste it in the appropriate window in the Plagiarism finder software. The program then scans the network for every word you have in the text and displays a result with the pages.

If the one who is writing for you is dishonest chances are s/he is lazy as well. Google some well chosen paragraphs to at least find out if it's being copied from another website, thats free and it worked for me.

A more ambitious swindler will use books and that costs more, do check it though or it's you that might get the stop order on your domain.

sure, if you google a part of the text there is a small chance that you find something. What if the text is rewritten from an already existing one on the web. How do you find that?

I have a free tool I use but they don't allow me to post the url in here.