it is possible. just don't click on any adds. you can sell stuff on ebay. but another interesting way is to make money off youtube! i know it sounds crazy but if you get popular enough you could make about 1 cent for every view you get (if you get popular enough) in fact, most of my favorite youtubers jobs are to make videos!
Well it depends what your doing. If you wan to sell something to make money then you probably will get the money. I do suggest using a well known site like eBay or Krag's List. f you wan to start a business online to sell things make sure you get the money before you give the product.