Elance no longer exists. They merged with Freelancer, and oDesk merged with Upwork. Upwork is a good place to go for freelance jobs.
Upwork still suffers from the same problems as the previous platforms.
For a starters, if you are a customer and you advertize that you need a sheep with five legs, you will see hundreds of applications and CVs of people claiming that they are sheep with five legs. Nature always materialize exactly what you have asked for. If you ask for people to declare that they are sheep with five legs and you clarify that you are willing to pay them for doing so, it is so obvious that you will receive exactly what you have asked for.
A second problem is that if you are a customer advertizing that you are looking for a sheep with five legs, there may indeed be such individuals around, few and far between, but they will not be interested in competing and doing a race to the bottom in terms of financial conditions, with people who they know, are obviously not sheep with five legs. Therefore, you are pretty much guaranteed that the real sheep with five legs will absolutely not be interested.
A third problem is that it is exceedingly hard to distinguish between people. No matter how you do that, people will always find a way to simulate it. CV? Well, no, in that case, you are only attracting expert CV writers.
A fourth problem is that the situation will easily turn into a business model where middlemen will bid on every customer request and out-compete the real workers, who are often less determined to spend day in day out in that kind of bidding contests. These middlemen will then only hire real workers themselves, when they have managed to land a contract. So, a customer will end up paying their budgets to determined middlemen, who will then try maximize their commission by paying their own workers as little as possible.
All of this, is not insurmountable, however. In the past, I have offered services on this kind of markets myself too. It just means that you have to be a battle-hardened naysayer who is used to nay-saying wars. It amounts to spending an inordinate amount of time proving that you have more willpower than everybody else over there. I consider that kind of situations with enormous proof-of-work requirements to be quite inefficient. It is worse than being a bitcoin mining machine. You will need to consume an inordinate amount of electricity to occasionally land a coin left or right.
The better strategy is to specialize in an activity that has very recognizable keywords. Then, post your resume in marketplaces that are much more specialized than UpWork. Whenever a potential customer contacts you, the proof-of-work characteristics of the situation will be much, much better. No bidding contest. No race to the bottom. Just a sincere conversation that could lead to a deal or not. If you just make sure that people looking for the keywords that you specialize in, can find you, you should be ok.