Alternatives

I don't see any alternatives, however what I would do is send them free leads. So they can check the conversion rate, and based on that you can set a better lead price. You need a call tracking platform to do this.

Try hunting for a call tracking program so you can hold them to their word should legal disputes crop up. However, I'd recommend not falling for it at all in the hopes of later winning legal battles. It should not come to that. If they're being dodgy like that just avoid it altogether. It's a man eat man world. There's a popular saying - There is always a fool in a deal. If according to you, no one is losing in a deal, then it's you.