I agree with Veinglory. I used to be on both sites when I was translating, and got a few jobs from Elance, but very little from Freelancer because everyone charges the minimum fee of $30 for even the biggest jobs, and when one does things by the book and quotes the real price they would charge, they don't even get a second look. When I found more interesting and high-standard translation platforms and got enough regular clients/agencies to work for, I gave up on those. I went back on the sites a while later, more out of curiosity than anything, and Elance looked like it had turned into Freelancer v2.0. And it's not just the fact that most people undercut your prices, I think people tend to expect a lot for little payment (e.g. 20x 500-word articles about XYZ that must be entirely original for $20 - it'd take you quite some time to research and write, for a payment that represents a couple of hours at minimum wage). There was also the fact that a couple of times, I got contacted on Freelancer to edit translations that had been made, after looking into the client's history of jobs posted, by an agency that was undercutting me on every job I applied for, and they were pretty much Google translations (I can't remember what it is now, but there was a very common term that Google could never get right and it made Google translations easy to spot). At that point, I felt that I wouldn't stand much of a chance because if I went by the rather good feedback for that agency, people were obviously not really interested in accurate translations (or didn't know any better). And that lowered the standard to a standard I wasn't willing to be likened to.
It's still worth having a look and trying, because when freelancing, every platform is worth looking into and may provide job opportunities, but if you have avenues that are a better investment for your time (as in you're more likely to get picked for a job) I'd recommend you focus on those first.
For what it's worth, I think I must have registered my details with the Freelancer website, because I received a payment through it once (or maybe it was paid via Paypal, I'm not sure, it was a few years ago now) and I've never witnessed foul play. Same with Elance (that one was definitely paid via Paypal).
I can't say for freelance writing, because I was a translator, but we also had websites that weren't for all kinds of freelance jobs but for translations specifically. Those had a higher standard, payment was fairer, and it's mostly from there that I got picked up by agencies that kept me over the longer term. For some applications you had to pay to apply (something like one dollar, or you could pay for a one-year membership), for others you didn't have to, but I felt that it was money better invested than spending hours applying for jobs I was never going to get. Time is money after all.
That said, last year, in France, there was an article on a legit news site about a girl who was making a very decent wage from translations on Elance, so maybe things have changed. I haven't been on there for quite a while, so I couldn't say.