Add negative keywords to project search and possibly to freelancer account for filtering projects definitely out of interest like "easy job", "link building", "clone site".  

... specially for users that invited a lot of buyers to the site. It's obvious I rather use the service than moving buyers out of SL.

Remove the reviews of cancelled projects. Programmer and buyers should only review if the project is completed

If buyer is allowed to escrow with poor rating it will be in high risk to get transferred once released. So, Scriptlance should ensure a risk free payment

Forcing NEW buyers to post projects limited to verified and certified freelancers will decrease the chance of failure for the buyer's first project.

This could apply to buyers who signup up within X days, or only for their first Y projects posted.

Display the Project Cancellation Ratio in anywhere in front page so that a Programmer can get an idea before he cancel any project . 

Display how many concurrent projects has the coder in hands. Its frustating to select someone and then realize that he is working in another 3-4 projects at the same time.

It happend to me many times, and I'm sure that other buyers should have the same bad experiance, to select a programmer and later on, to find him working on other projects too. Result? Getting emails from the programmer asking for something that is not on my project, or big delays on delivery. Worst than all (that's why I'm asking to not allow bids in other projects), when you face the problem to have the coder disappeared or delaying in replies, because after eg my cheap project of $100, he awarded a new one of $1,000.