If we don’t water well the soil around the new tree will suck the moisture away from the tree.  

Even if you put down a good concrete sealer/vapor barrier you run the risk of getting moisture up under the flooring. 

No moisture wrap, no redguard needed.

If it localize, i.e. a roof leak in a certain area, a wall in a basement that have moisture coming through.

That could be a moisture issue as well.

One home with a dog hadn't changed their filters during the winter; the unit worked harder and actually had moisture in the return because of the temperature differences. 

Read your contract through, as many standard contracts do have built-in protections that if termite/moisture or lender-required repairs are found, seller agrees to cover up to x% (and it usually states, if no number entered, parties agree to 1% of purchase price). 

Turns out the builders buttoned up the walls during a storm while there was significant moisture present and now the insides of the walls are full of mold.

Now they've decided to go to this Coretec product at $3.2/sqft that supposedly is fully waterproof, needs no moisture barrier, can go in kitchens and bathrooms, floating floor no glue required.

Older home have the potential for higher repair costs due to outdated electrical, plumbing, etc, but as long as there's no moisture issues these houses were built 10x better than today's houses.