In my opinion, Grant Cardone is a snake oil salesman. 

This is primarily due to the low oil prices at the moment.

And again, it seems as though there are many directions these billionaires have taken in their lives from technology, retail, telecom, oil, stock trading that have gotten them on the Forbes list and to say that one way or the other is foolish would be pure fiction.  

Free oil changes?

I just got back from Edmonton and there's a lot of pain, but I'd wait 6 months to see what happens to oil prices.

I was nervous initially thinking that I was sold snake oil.   

Rental cars get oil changes and detailing regularly and are in impeccable shape for purchase (they don’t use them after 50k miles).

Or do you mean that: " If the tenants put a bunch of oil/dirt/etc on the walls it will easily will wash out?".

And, this involves everything you care about:  stocks, real-estate, business dev, commodities (oil, precious metals, minerals, etc), estate planning, asset protection.  

Traditionally it's been more of a boom/bust affected by Oil+Gas.