if you can provide volume to the customers (which, eventually they will want - or if you plan on expanding your lead sales to more than one company) - throw them a few for free.
Hit them up after you've given them enough time to follow through with the leads, and question them about buying more. if the company is worth their weight, and your leads aren't absolute shit, you should be in business.
Another method is to just get your foot in the door with another product or technique, and approach them about leads after you've already built a general rapport with that client.
either way, just get in front of the client, tell them what they want to hear, and make them bite. If they want nothing to do with it - or have a foul taste in their mouth because the last time they bought leads through "salesgenie" it just didnt work out, fuck off and go see their neighbor.
this is social engineering, it isn't rocket science.