Leads are, in a sense, the life-blood of your business if you're building by attracting those interested in a home-based business opportunity rather than simply by promoting your products and gradually turning regularly re-ordering customers into distributors (we do both).
It doesn't actually matter in principle whether they're self-generated leads or bought-in leads - they're all "leads".
I use mostly self-generated leads and have, overall, done better with them than with bought-in leads, but I have used bought-in leads on four (or possibly five) occasions over the last seven years and done ok with them, and may do so again some time in future.
From my own experiences with bought-in leads and those of others in my group, my little tips about buying leads are something like as shown below (all opinion, of course) - some of them are based on ensuring that the people concerned are genuinely already looking for a home-based business opportunity (if not, they are not "leads" in any meaningful sense of the word):-
(i) You need to check the type of wording to which they have responded ("business opportunity" type of wording is good, "work-at-home" type of wording is useless: you can sponsor these anyway but a high proportion of them will drop out pretty quickly because they weren't really looking in the first place for a "business opportunity" per se)
(ii) They need to be relatively recent
(iii) It's better if they have not yet been contacted (from that source, anyway) by anyone else offering a business opportunity and will not be sold to more than one other person
(iv) Phone numbers are essential: there's little point trying to do this by email
(v) They must not have been incentivized in their collection-process (people wanting a free entry to a prize-draw are not "leads")
(vi) They must come from a reliable source which you or people in your company have previously used beneficially
(vii) They must not be sold by an MLM-based process in which others in anything like an "upline" are earning commissions on their sale (the prices will be artifically inflated to allow for the payment of commissions and a high proportion of these, in practice, will turn out to be "business opportunity jumpers", too)
I have had much better experience with leads costing about $5 - $6 each than any other, cheaper types, though obviously there's quite a lot of luck in it.
My self-generated leads are roughly on a par (in overall quality terms) with the very best leads I've ever bought (which were $8 each) and they cost me a lot less than that to generate. So mostly I just use my own. But there's nothing "wrong" with delegating/outsourcing the lead-generation function of your business to a specialist - if you can find the right one.
My overall impression: don't expect very cheap leads to turn out, in the long run (though they may appear the opposite in the initial stages when you sponsor some of them) to be anything much more than a waste of time. Just my perspective.