Rain for extended periods or broken pipes and wet soil the support sinks in the mud and sags start and trauma finishs itI have seen lumber twist, split, fail, and turn worthless in a building. 

@Sandy Hatch I haven't heard anything about them but I've read a lot of good thing things about http://www.thertastore.com/ and have been researching them.

Is there soil issues or is it more like faulty/leaky basements?

Admittedly, I stopped reading this thread several posts back .... but personally, I would tell the tenant " to go pound sand! " I

The cost would be soil treatment and tent for about $1350.00, which I am trying to get the seller to split the difference with.  

I was confused by the narrative which said something like "just a few steps from the white sandy beach and crystal blue waters of the Caribbean."

With that said you will need a soils report and possibly an engineer for the foundation.

If there is waterlogged soil outside the foundation with all of that rain, the pressure increases with depth, and it's pushing its way into the basement through the Drylok.I agree that if it's just wall moisture and that this is an outlying event (i.e., you very very rarely see these 8"+ rain events), you might simply dry things out and recoat.If it's likely to reoccur, french drains are an alternative.

Depends on the location this may be real hard soil or in South Florida it's mostly easier to excavate sandy soil. 

The East side is all red soil that  looks like Tahoe and the Western side is all green lush vegetation.I have sold property up there as fast as I could list it but trying to get a Santa Rosan up there to buy and live is tough with the commute, though many more do it now than 10 years ago for sure.