While working as an online freelancer on Fiverr wasn't completely horrible, it definitely wasn't anywhere near the best experience I've had. Freelancing is, understandably, competitive and can make it difficult to find something suitable or obtain it. There are hundreds, if not thousands, of graphic designers, photographers, writers, and even narrators on this site, (so, mainly for people working in the fine arts industry).
However, I've had experiences with clients that never paid after I finished completing a project for them. The payment system on Fiverr also takes forever to process and can take up to a few weeks to almost an entire month before finally receiving a deposit in my account. There are not many job opportunities on it for a generalized base of freelancers and not enough clients to provide financially. If you're looking to make an extra couple of bucks, you can certainly give it a try. But, if you're looking for a site that provides you with a steady source of income, I would not recommend Fiverr at all.
Good for artistic freelancers, offers their own healthcare
Not enough opportunities, bad clients, etc.