When a post is an extract from another site, written by another person, I acknowledge that person with my "...read more>>>..." link at the end of the item. A link which when clicked leads you to the original article from where my article is taken from.
This method is accepted on other web-sites and blogs on the internet. So why not mine????? If my web-site is to be reported to Google for 'plagiarism' then so have thousands of other sites too.