Facebook used to be an easy source to tap into, but since they have formed a public company with shareholders who need to be kept happy, Facebook have changed their Terms of Service several times recently and have clamped down on a number of things that used to make lead generation relatively easy. They have discouraged siphoning off clients to external web sites and CPA offers, and have raised the cost of advertisements that do this. It remains a viable lead source however.
That is why we actually had people order leads, and we called them. We called more than one bunch of leads as well. This at least would give us a feeling of consistency or lack of it. The MLM Lead companies we chose were highly consistent in quality of lead, and people who truly were looking for a business. It took us 7 months to complete the research on MLM leads.