Listing sources in a book...

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?

I'm no law expert, but I would think if you cite properly, you're fine.

Thats what I figured. I'm in no way almost finished, but I'd rather do it right from the beginning and have less to fix later on.

It'll never get printed as a book-book, I'm just gonna make it a PDF to print and sell for $5 on my ebay account or something XD