Stack Overflow rep is already used to determine when a user can do things like edit questions or moderate - why not use that to determine who might be a "serious" candidate? Just like you have metrics that must be met to moderate questions, why not add one that lets you add your CV for free? Maybe there are breakpoints where it gets cheaper so the only ones paying full price are people with little to no rep at all.

I really like the idea of the site learning who to trust over time - while I wouldn't say it's fully accurate it's working towards the idea at least. This is just another area where you can implement that idea.