Looking for a US notary in Zihua now

An illegal notary is like no notary at all. Simple. A transaction requiring a notary would be null and void. Documents useless, worthless. KNOWINGLY using an illegal notary would of course be a violation of the law itself, so the other party could easily sue and win for attempted fraud or fraudulent representation, for example.

Let's suppose a real estate transaction has occurred. A house is sold. A new mortgage is attached to the house. The seller has received a significant lump sum and has used that as the down payment for a bigger home with a mortgage of its own. A year later, it is discovered that the buyer used a fraudulent notary from Zihuatanejo. What would happen?