I have a few websites from customers that have (partially) the same content as other websites. I plan on rewriting all content that is not original, but how do I know if my websites have original content, or content that's been copied from another website?
My customers say all the content is original, but I have my doubts to be honest. They often let other people who don't work there anymore write content for the sites.
What I did so far is copy a line from my website that can be found in other websites as well and pasted it into Google Search. If my website is the first link, would it be considered the original source?