I've written online since 2005. Editorial demands differ depending on assignment requirements. One assignment dilemma wreaks havoc: rehash vs. virgin content. God forbid any site admit to rewriting content. It sounds unethical and plagiarized. But that's exactly what editors expect writers to do.
It's common knowledge that quotes must be sourced. You can't say something someone else said without giving them credit. You can't copy the bulk of your article from someone else even if you source. Only 5-10 percent at most or it will be plagiarism. But professional articles require quotes and sourcing. Editorial Conflicts: the Virgin Content vs Rehash Dilemma