We use Experian's Knowledge-Based Authentication, which is similar to what ben1040 mentioned above. It is based on your name, address, and sometimes your SSN.
You can read more on Experian's KBA here: https://www.experian.com/products/pdf/knowledge_iq.pdf Or here: https://www.experian.com/esolutions/esolutions/products/frau...
Experian's KBA is not adequate to prove identity for legal purposes in any state, or for federal purposes. My banks won't even use it to verify identity for credit purposes.
What incompetent lawyer told you that you could use it for the basis of your service? Moreover, what incompetent lawyer told you that you could offer such a state-specific thing as notarization services nationwide?
The credit bureau services used by banks are not intended to verify your identity for notary purposes; they are used to verify your identify for credit purposes. The databases provided by the credit bureaus are so unbelievably error-filled that they frequently fail to perform even this basic task (and if you read the fine print when you agree to allow this type of check, you will see that they acknowledge that their service cannot be relied upon to prove identity).
Moreover, this system of "verification" merely proves that the person being examined knows publicly purchasable facts about the alleged identity they claim. (All of the data used by these systems comes from public records, all of which can be accessed for free or for a fee.)
But I assume they might use one of the schemes used by banks when setting up online accounts, or even by the TSA when you forget your ID and want to board a plane. They look at public/commercial records to come up with questions that only you should be able to answer.
Stuff like "DMV records show you own a Toyota Camry, what is the model year?," "which of these best describes your monthly payment on your mortgage?" or "which of these lenders holds one of your student loans?"