I've used elance as a buyer and was very satisfied with it. You can agree whatever terms you wish. I had a portoflio presentation before jumping in to ensure the style of offering (design) was in line with what I was looking for. It isn't all price. You have to read their credentials very carefully to ensure they've got the exertise yo need and can do the job in the time frame required. So the flipside is to ensure you write your creds very carefully and present with a slick set of examples. Hope that helps.