If (any) result is returned, you are charged. I just checked my waterfall and it goes like this.
The first step of waterfall run and I was charged, I used find and validate phone number combo.
The next step says (and I wasn't charged because "run condition not met" as I already had data) - The condition is false because the "Find Mobile Number & Professional URLs" field exists and has a mobile phone number ("123456"), and the "Validate Clay Enrichments" status is "valid." To make the condition true, either the mobile phone number must be missing from "Find Mobile Number & Professional URLs," or the "Validate Clay Enrichments" status must not be "valid."
(I hope this all makes sense 🙂)