One was to dig it out and seal it. 

I know the ceilings and walls need to be sealed, primed and painted.

This pooch also dug many holes in my lawns and they had to be patched and re seeded.My floor guy says since the carpet was four years old I should charge her 75 percent of the replacement cost for the carpet and pad plus full price for the clean up and sealing of the floors.

The fix basically seals the floor of the basement, sucks the air underneath it and blows it out the side through a tube/fan combination.

I almost bought a condo there across the street from the beach right on what was the Seal Beach border.

If I was in that situation I would figure out where the water is coming from- Seal all cracks add a sump pump and dig down outside and waterproof the house.

That is, it has to be fully sealed from the elements, have running water, heat and air, the basics.

Not having any tax headaches because it is or was recently my primary would seal the sell deal. 

If he has been living in the house for 20+ years and is a moderate to heavy smoker, there may be rooms where scrubbing, sealing and painting simply won't keep the chemicals from coming to the surface and you will end-up pulling down the drywall and hanging new.We renovated a house some years ago where the former owner had a favourite chair in one corner of the living room where she sat and smoked.  

My attorney said it would be throwing good money after bad as they have their contracts sealed up lock, stock and barrell.