And how would an exterminator know anything about how to fix it, what the extent of damage is or how much it will cost?
If I was your son I'd pass on the house or if he's buying it real cheap make the owners fix and pay for it and be there to see the extent of damage before making a final decision.
Termite damage can get real expencive real quick.
How does this guy think they got up into the walls? There sure did not hitchhike. They had to eat there way up from the gound, though the fondation plate, the rim joist then into the walls.
What type of siding is there? I'd be pulling some of that off also, looking under the house as well, as the inside walls.
Fiberboard on the walls
That's got me worryed. I can not think of anytime any form of a fiber board would be a sutable inside wall surface.
Back in the 70's it was used as sheathing, not used anymore because it failed so bad.
He found damage in serveral rooms, but thinks it's new damage and not all that serious? That's nuts, they would have had to be there a long time to have done that much damage.