Alright, tell you what, let's compare numbers.
You made $1000 this month at $0 tax liability.
My way:
Unit A rented @ $1,000 mo
Unit B reduced so that it can be rented @ $700 mo
I've made $1700. Let's say that I'm paying 20% tax rate - now you KNOW that he's not paying no 20%, but let's be harsh on me to give you the advantage.
After taxes, I made $1360. I make $360 more than you each month.
OH MY GOD, MAGIC! HOW DID I DO THAT? I PULLED OUT MORE MONEY FROM THE SAME LAND AS YOU
AND bad news for you, during your tax audits, your auditor goes "wait a minute, there's a similar unit in the same area that's rented for $700. That suggests you overvalued your lost income for your unit."
Now you're going to have to do your taxes again AND pay a penalty - ALL DURING WHICH TIME I'M MAKING MORE MONEY THAN YOU ANYWAY!