I would personally be very skeptical of the leads genreations people without some serious qualification.
My companies have been around for 10 and 14 years respectively and we have 1 salesman who can actually open the doors and get us the meetings we need. He is employed full time now but there have been many who have tried to claim that ability.
To address your real question is how do you work out who to work with ... I can't say, its a matter of talking to a range of people and hear their stories, actual deliverables, actual experiences VS "almosts" OR "could work if" are a big give aways ... or setup the deal such that if they actually deliver an income stream to you then they deserve a payment otherwise perhaps its not ... the trade off to that is you need to invest in the months and years of getting into some big players before the payoff occurs and you have the runs of the board that allows you to grow.
- The question is are you willing to bet on this person?
- How are you betting on this person? (Paying their wage OR paying for the result).
In the end the real answer is you have to roll the dice and hope you have a good one ...