Do they already have other properties producing rental cash flows?

blindly sending mailers to a whole zipcode is going to produce sub-optimal results and cost a lot. 

But online lead sources produce at like 4%.

Split the solar array into 4 equal parts and Put meters on each unit and charge tenets by kWh produced by solar at or under current rates and for excess provided by the electric company at standard rate. 1b.

You want to know how much cash flow it will produce when you are no longer there. 

@Alexander Sheridan how much total rent are you producing from the 7 rentals?

So a general rule of thumb would be that if you're deferring more than $40K - $50K of gain then the reverse produces a net financial positive to you. 

As with most things there's usually a way to get square footage for less but just like produce that's been marked down because its about to spoil, you'll want to consider why things are below market rates. 

If you are purchasing this with the sole purpose of a tenant paying down much of your debt and not producing income, it is an option.  

Learn the market there, understand market price, run the numbers to confirm the typical property in that market at the typical price for the market will produce the returns you want.3.