Buying full articles on another websites

I´ve seen many competitors buying full articles on another websites, where they can put a link to them. How safe is that? So far the websites which i spotted doing it, are growing positions without any penalty. The articles look very natural because the full article is talking about a topic related to their linked site. Is that a normal practice? its not nice to talk about, but it seems like everybody is doing it. There are some fields in which getting natural links is almost impossible