Elance is a legitimate site. The big three for hiring freelancers are *****.com, Elance.com and freelancer.com. There are many good developers on all three sites and also some scammy ones.
For best results:
1. Setup a clear project summary. Make sure that you detail all the changes that you need.
2. For small projects, use a fixed price contract.
3. Document everything on site.
4. Do your homework when you hire. Look for freelancers who have completed lots of projects and ask good questions when they place their bid.
5. Test, test, test your work.
I believe that Elance.com is a reliable site but, even on legit sites there are still chances of getting scam. One of the best things you could do to before hiring a web designer is to test them first. You could conduct an interview and ask for some references, which help you assure that the person you’re going to hire is thrust worthy and competent for the job. However, looking only in one area will tend to miss you great talents and skills. Try to expand your search on other sites like Staff.com, Guru.com and even on job boards like Craigslist and Monster.com. This also helps you find the right person for the job.