It may be possible to repair the foundation but you would also need to address the leaking.

Gnats in the kitchen and bathroom she says the gnats came right after I fixed the leak under the kitchen sink but there in the bathroom also ( what I have investigated being dirty will attract gnats and roaches in a heart beat). 

The tenants are often great people but they often live paycheck to paycheck (like about half the country) and they may lack other skills that can manifest themselves in all sorts of ways (be it communication, ability to handle the clutter on the porch, or afford to fix the car leaking some oil on your driveway).In fact, I see about 3/4 of the conflicts for landlords on BP relate to items like late payments, tidiness, a broke this or that, pets (or family members) run amok, getting along with other tenants/neighbors, not following rules, noise, smells, problems with move outs, or even issues with applicant pool (like credit or job history).When you step back, you have to realize if they (all your tenants) had excellent financial, interpersonal, communication, and organizational skills--they may not be renting from you (but own their own place or even their own rentals!!).

Conversely, if you're looking for quirky zero-down, owner-financing, you might have to pay over what the free market would bid on it's own.Side note, there are probably more than three components but I like to keep it simple for iPhone replies with an array of likely spelling errors.

In my case they would not pay for the Plumber who repaired the broken pipe, but they did pay for all the damage caused by the leaking pipe.   

When they did this, I've been told it caused it to Completely freeze up and leak.

I called Dee technician and they said it's old machine and might be leak in coil.

As far as REI, I wouldn't even take it into consideration unless you're investing in parking lots.Remember - the iPhone has only been out 10 years.

Will you find that the vacant property had a roof leak that went unnoticed so flooring is destroyed?

The problem with asbestos is there is no escape, it is not like a plumbing problem when there is a leak, someone else can fix it. there is a ton of paperwork needed to be done, and the disposal chain of custody report plus air quality test result is your only ticket to get away with liability.