I feel like sites like Elance just foster bad client-developer relationships from the get go. With everything being so prix fixe it sets aside the #1 attribute

I feel like sites like Elance just foster bad client-developer relationships from the get go. With everything being so prix fixe it sets aside the #1 attribute of software development - uncertainty. From reading this post it sounds like everything was honki-dori until the client came back with changes. Changes equate to more development which equates to more money. Clients need to understand the uncertain parts of software development better and paying up front sites like Elance and others just don't support that.