When life give you lemons, make lemonade.
I had a similar experience last year. Found a 04 Tacoma on CL, frame was rusty, mainly surface but no holes. Later on found out that the mfer that sold me the truck filled three rust hole with bondo. I had Jon of Moorespeed Motorsport patch the holes up with metal plates. Did some deferred maintenance on it, drove it a year, took the SC off of it and sold It to someone that loved it.
Chalked it up as a learning experience and move on. Good luck to both parties.