People search for an "I-9 notary" or a "notary for I-9". The phrase is understandable and wrong. USCIS says that when an employer uses a notary public as its authorized representative, that person is not acting in the capacity of a notary, must perform the same steps as any other authorized representative, and should not provide a notary seal on Form I-9. Completing an I-9 is not a notarization, and Form I-9 does not get notarized.
That changes how you work at the table. No seal or stamp on the form, no notarial certificate attached to it, and nothing on the confirmation or the invoice that calls the visit a notarization. If a hiring manager asks you to "notarize the I-9", say no, explain the rule in one sentence, and offer to complete Section 2 as the employer's representative instead.
Your commission still counts in the sale, just not on the form. Checking IDs and keeping appointments is already your daily work, and an HR manager can see that. It gives you no authority under the I-9 rules, so don't let anyone treat it as if it does.
Federal rules are not the whole answer, because the state that commissioned you can restrict the work. California is the clearest case. The state's official notary newsletter told California notaries in January 2020 that a notary public who is not also an immigration consultant is prohibited from completing Form I-9, even in a non-notarial capacity and without using the title or the seal. Under California law that status means being qualified and bonded as an immigration consultant, which includes a $100,000 bond filed with the state, a background check and a disclosure form.
California is not alone. Montana's official notary FAQ answers no when asked whether you can complete an I-9 because you are a notary, Maryland's says a notary may not verify the information on one, and the District of Columbia's notary handbook says a notary public may not assist. Pennsylvania and Oregon take the other view: a notary may do it as the employer's representative and not as a notary, and Pennsylvania adds that no notary title or seal should be used. Check with the office that commissioned you before you offer this service.