One of the main reasons why mediocre recruiters don't get to know the candidate is that they are completely focused on the job to fill. They need to know you only as much as it would take them to sell it to you.
An agent would get paid no matter what company he ends up placing you at, so there is a much higher incentive to understand what you really want to do.
I also think there is a lack of objective information on how a company is doing. They pump out information on how they are "crushing it" and how everything is going great. And Glassdoor is usually filled with bitter employees with an ax to grind.
So some thorough checking through backchannels would be incredibly helpful. Not to say you couldn't do it, but as a recruiter I have never seen a candidate do it.
Yes, you would have to assume a 90 day guarantee, similar to the classic recruiting model. One of the issues with charging an individual is that they often don't have $25k in extra cash flow. That would require a payment plan of sorts. In any case, I appreciate the feedback.