There is one downside with RentACoder though, and that's that you won't win any jobs without having first complete a couple successfully. It's not the end of the world - find quick and easy tasks, explain that you're looking to build up your rating, and offer to do them for $3. It does mean that you'll lose a day or two of income though. Once you have a couple of ratings though, the only way is up! :)
Don't back off from bidding higher than the disered "quotes" mentioned by customers. Once I went for a designer who was quoting more than twice my initial upper limit for that job. when I looked at his profile, he had a very, very long portfolio of his freelanching designs as well as designs he worked on for customers. He had a lot of very high ratings from his past customers and he justified/explained in a similar way that motothemax mentioned about why his rates were higher. Another thing was, he was very professional and upbeat throughout his communications.
So if you did be interested in some feedback on deciding priorites of a customer:
1) Portfolio 2) ratings from past customers (here the readiness to work initially for lower rates, may be usable sometimes) 3) scores on Odesk tests and the distribution of those scores across different tests - its not perfect system, but its better than no scores