I had a cost seg done on one of my homes and trying to get one done on another from this company that rob with bigger pockets had done a set on.Every time I email them it says there email doesn't exist and cannot get a response.

Saika  While a permit is a hassle, what happens if there was a fire, it burned down, someone got killed and the fire department was not even aware the unpermitted structure existed.

This is the investment thesis in my area, it is becoming a bit saturated, but if you can rent just below the new build/corporates, and maybe accept tenants that are a bit outside of the corporate approved model, you can keep your place rented. 

As others stated, if the existing structure is legal but non-confirming that should not be an issue.

They did, in fact, provide a money-back guarantee if it did not outperform the market in a one-mile radius, which in my case is a really well-performing area that is borderline saturated.

So I'd be doing my best to get the highest possible rent/revenue but without needing or counting on that.What you refer as cut-throat competition exists in every market where you have demand.

How much "fat" do you believe still exists within that? 

Are you taking this subject to existing mortgage?

 I'm not opposed to subject to, but my fear is whoever I am taking over the existing mortgage from will not continue making the payments.You make the payments.

You can do this with a simple, one-page addendum, or even a written statement added to the existing lease and signed by you and the tenant.Example:This lease agreement is hereby amended to reflect the change in ownership of the rental property located at 123 Straight Street, Cody, WY 82414.