I’m working as a coder for about 5 years on e-lance web site like rentacoder, scriptlance, getafreelancer.
When a buyer it’s just describing me what he wants just with words, it’s making my job twice harder.

If you want to post your project on a e-lance web site ,a very important step is to make a design document where you explain every feature your software should include, take time and make this design document as complete as you can, because not focusing enough on this important step will cause a lot wasted time trying to explain the coder exactly what you want.

You should provide a sketch for every screen you want your software/web page to have. Every sketch should include all the buttons that screen will include and what should those buttons do.

You should find some similar products and show them to the coder, telling him what you like and what you don’t like at each of the provided examples.

If you want to outsource a “big” project you should choose a coder with at least 10 ratings, you don’t want to work with amateurs because amateurs can make you life really hard, providing you cheap results that needs a lot of changes this causing wasted time and time means money.
If your product it’s a small one ( let’s say under 50$) you should try to work with a coder that has one or two ratings with a good portfolio because he wants to gain more ratings and will focus all his time and work over your project and please you.
I’m giving you this advice because when past clients are asking me to help them with a small projects, I’m not focusing all my attention and all my time for that project and some times the product it’s suffering a lot of changes.

I always recommend rentacoder to my friends, on rentacoder you can find without problems a well rated coder with similar experience as your project involves.