Most HVAC leads are shared. Angi, HomeAdvisor, Thumbtack, Networx and the other pay-per-lead networks take one homeowner form and send it to three or four contractors at once.
All of you call within ninety seconds. Whoever picks up first or quotes lowest wins. You paid the same either way.
Shared leads cost you three ways at once: you pay per lead whether or not you win it, you win a smaller share of them, and you win them at the price the cheapest contractor set.
Industry data puts close rates on shared leads at roughly 10-15% - each lead is sold to three to five contractors at once, so the math works against you before you pick up the phone.
An exclusive lead takes the race out. The homeowner filled in one form, it came to you, and nobody else got the call. That is the only thing it changes, and it is worth paying for. It does not decide who the homeowner hires. You still have to answer fast, quote fairly and close the job.
One more honest point. An exclusive lead is still a lead you buy. If your trucks are idle next Tuesday, it fills them. But it's a faucet: when you stop buying, the leads stop. If you want calls that keep coming after you stop paying, that's the channel work further down the page.