Citations aren't simply about adhering to law. They enable people who want to read further to do so or verify that you've interpreted your source correctly. They also make it clear when you are expressing your view or stating generally accepted information. While this is essential to academic style writing, it isn't such a deal with less formal writing or for news. To some extent it's a style thing - a blog that's written more formally will err on the side of caution when it comes to offering references.
I thought every fact that you got elsewhere had to be acknowledged with some kind of citation. The topic I'm writing about is one I know nothing about prior to research, so anything I write will have come from a source.
Even with academic style writing, you wouldn't normally cite anything that could be interpreted as common knowledge for those who know the field. Just because the info is new to you, that doesn't mean it can't be regarded as 'common knowledge'.
You do need to cite sources for direct quotes and information such as data, and you might want to point to a source for anything wildly controversial or unusual, but it isn't necessary to list every single source you've used.
However, it's a sensible move to keep a note of all sources even if you don't put them in the piece itself. Then if you do slip up, it's easy to make a correction.
And the very fact you're asking such a question suggests you should be charging more than you are.
