Friends of ours have a son in Austin TX looking for a house.(We've known them more than 25 years since our kids were in grade school together and we parents get together regularly still).
I'm very familiar with residential foundation issues due to moisture sensitive clay but around here (Southwest Ohio) those problems are relatively mild compared to Texas and other places. I'm trying to give guidance to them so they know what they are looking at. Ultimately, they will need a good local structural engineer to get their "eyes" on it but in the mean time I'm wondering:
For a house built on a slab foundation around the early 1980's with 3" of differential settlement and drywall cracking throughout some areas of the house, is it likely that the house was not built with a post tensioned slab and is it also likely that undermining or piering is going to be difficult to do well?

I'm just guessing that waffle slabs are more common now but not so common 40 years ago.

I searched for "foundation repair specialists" and I see the same franchise names in Austin that I see around Cincinnati (along with some mom and pop sounding names). I also see some engineering firms that do foundation inspections but as in other places, I'm not sure who is capable, and not tied to a foundation specialty firm too closely (maybe "honest" is another word for that).

Any thoughts?