Avoiding plagarism is really easy: just make sure you only use content where the author has given permission and a licence, or write your own!
In many cases a site that deliberate steals content will have spent more time on SEO than the original author, probably because the author had to write their own content. The other annoyance I've seen is where a university, or student, with a ,edu or .org account copies an article because the .edu domain name has such clout it ranks higher even when the other article is older, and the author's name is on the stolen work.
Google makes it very hard to lodge DMCAs to get this content penalised or taken down.