Without lead qualification nothing you buy referred to as a lead leads anywhere.
Lead qualification is a process custom-designed to meet your business' particular needs. It is pricey to pay someone to cull through a bunch of "leads" that you buy in bulk from some service provider. But without putting effort into qualifying these contacts, you'll get only your money's worth.
I would start with buying only what I can return if the quality is so poor that I might as well have thrown my dollar bills into a fire pit. That's why I prefer to rent lists rather than buy them. By renting them, only those who respond to my promotion become part of my house list. The rest I only pay to use for 1 instance, which is far less costly than buying them for good.