Quick background, last year was my first year of real estate investing and long story short I pulled the trigger on 2 STR properties at the end of the year.  Now I'm slowing getting all my tax docs ready for my CPA bu...

Seller financing can be a form of OPM in a sense, but you still need a down payment and other funds in many cases. 

I just wanted to add:The new Ordinance from City of Jackson Mississippi requires registration of all rental units, the payment of an annual fee of $50 per rental unit, annual inspection by the city, fixing any inspection issues, a fine for late or non compliance.And, it requires out of area owners to have a local PM or agent.I believe the fines can run to be high dollars.

Seller financing, no down payment, 3 yr fixed at 5% balloon.

Say 243-147= 96k over 30 years is a 3.2k/year benefit, obviously more benefit with higher monthly payments.

Also Fannie Mae just introduced 5% down payments for owner-occupied 2-, 3-, and 4-unit homes.2) Home with attached or detached casitas These types of homes are popular in Southern California and you're able to live in the main room and rent out the casita. 

A personal loan is not attached to title in 2nd lien position and you can get up to $50,000.00 if you have good credit and your DTI is in align.You can also use that $10K for a down payment on another purchase so at least you have options!

So if the delta on your savings versus interest costs is only 2%, and it appears you're a RE professional, your tax advantages will probably make that a wash meaning there's no advantage at all to spending all your cash unless you are just afraid of making a payment. 

Forsimplicity’s sake, we’ll say that the seller will pay our closing costs, whichmeans we are required to put down $16,000 for a 20% down payment.

I run the numbers all the time on these types of deals and they rarely pencil at at the seller's price AND today's interest rate and down payment.