OP, why didn't you immediately give more information and not make it conditional on registration? For example, the price of one check can be found out only after registration. Also, I didn't find anything about the methodology you use or what the report contains.
Even if you are an established service, there is no reason not to publish such information.
I could use a fancy email I only open to verify the email.
What good does that have?
That's still more work for you than just switching browsers or renewing the IP. So, it is obvious that they want to reduce to a minimum those who would exclusively use free queries.