What are the rules and guidelines about making and selling your own skin care and cosmetics? For instance, if I made a facial cleanser could I sell it on eBay or somewhere similar if I listed all the ingredients? How would this work?

As long as the ingredients are cosmetic safe. See the FDA website for lotsa info. I make b&b products and some eyeshadows once in a while and sell them. There's a great forum at one of the supplier sites. You'll get tons of help there.
http://www.tkbtrading.com/display_page.php?i=28

Sounds like something that needs to be fda approved.