If I require a credit score of 750, that would dramatically reduce my risk but it's still no guarantee that they'll be great tenants.

Section 8 is somewhat guaranteed income, but in some places attract the worst of the tenants.

As we all know, investments come with risks and no return is guaranteed.  

So now I am occasionally vacuuming, and waiting to see if the fleas come back.The exterminator provided a 60 day guarantee.

Since no paychecks are guaranteed I’ve decided I needed “x” months saved.

Retired parents have $1M liquid cash in the bank, looking to buy a $500k home with 20% down.Clearly they have enough to buy in cash, but the plan is to use other peoples money and have the rent cover the monthly payments.There's no income, but if banks could somehow quarantine some of this liquid cash each year, they would guarantee no default in payment.Is there a low interest rate loan they can get?

Typically yes, you’ll be signing a personal guarantee, so it will affect your credit and DTI.

It's no guarantee but it's a good place to start.

However you will not be able to get a guaranteed price until they visit the property as a GC will see things you do not.

I guarantee 1000% you will regret not buying it!