So, I've started writing a pamphlet/book/guide. Kind of one of those "for dummies" books.

Most of the book I am writing from things I have learned over the years; I can't find exact sources for them other than my own personal experience. I have explained that in the beginning of the book.

However, there ARE things which will require a source (hard facts, quotes from historical figures, etc).

If something is available online as an encyclopedia or webpage of information...am I allowed to use these things as a source without having to worry about getting sued? I'll obviously give credit where credit is due...but is using websites for something I plan on selling (although, for a very low price) gonna get me in legal trouble?

Does it vary site by site?