As interest rates decrease cash on cash increases  both due to the fact finance charges are lower and as an indirect consequence you can often obtain higher leverage (meaning less cash invested) because the 1.2-1.25 debt coverage ratio most lenders seek as part of their underwriting takes into account interest payments.

The previous landlord only collected half month rent as deposit, and I would like to increase the deposit to standard one-month.

The more impactful thing is the rapidly increasing amount of competition in the form of # of Airbnbs in existence.

Quote from @Andrew Steffens: I have no idea who that is hahaI have seen an increase in this (like everyone else) because Airbnb spoils guests. 

However, once converted to personal use, you can no longer claim depreciation, and the accumulated depreciation will reduce your adjusted basis, increasing your potential taxable gain upon sale.

This equity capture can increase your net worth big time.

You could restructure the contract to increase your protection, but the seller won't like that.

The allure of fat cash flow (at least on paper) and the low barrier of entry (down payment) never stop attracting new investors. 

I am working on increasing my knowledge and skills on the accounting side of investing.  

But I'd like to see Lynnette's projects to support your claim "the portfolio was a 30% increase in cost to the consumers" since in TN, NC, VA, NC PPAs are priced at avoided costs.