Hey Joe, One thing to remember with a home inspection is they aren't town inspectors looking to make sure everything is to code. Home inspectors look for safety.
If I was evaluating that property, a couple of things would stand out:
I agree the 5" slab probably isn't sufficient given the potential for freezing and movement under the slab. One of the pics looks like there may be some water erosion from under the slab. It's a bit like a safe harbor statement - just because it hasn't happened, doesn't mean it won't in the future.
Also, the 4x4 supports don't appear to be on cement footings (down to frost depth). They may be pressure treated, but even pressure treated is susceptible to rot over time.
The cement brick under the house appears to be layers, but not mortared.
The pic that appears to be under the decking, the randomness of the 2x4 would be a question for me. It looks like they are there to reinforce the decking, but there are no joist hangers or cement footings (down to frost depth).
For me...I would have a structural engineer come out and evaluate the footings of the buildings to ensure it's sound.
Good luck in your search!