I had a Pinto around '80 that looked OK, but the floorboards were totally rusted out.
If I sat in it, the floor would go down about 2" and it felt like I was going to end up on the road.
I had put 1/4" plywood pieces down to keep out rain and dirt, but I never repaired it properly (No time: I was working, building a house and in grad school).
The car ran great but I eventually put the car up for sale. A very big guy (approx 350 lbs I'd say) came on a snowy New Year's Eve and bought it for $200.
I warned him about the floor, but he was pretty nonchalant about it.
Wonder if he made it home?