@Ali Aldhanhani - Hi and welcome Ali....  1 - On a standard real estate investing calculator "vacancy" is expressed as a percentage rate and is understood as a "negative income - or expense" - and helps you be realistic about the amount of rental income that you can expect from that unit during the year.

They understood the publication and were confident that I did intend to occupy the property.

I was a high volume RE agent for years and never understood it the way you described.    

It sounds like you have the DP, rates, avoiding inflation understood, is your biggest issue the inventory? 

In this case, this person has the discount points section blank, implicitly that's understood to mean if they can get 3.5% via paying ANY amount of points (presumably up to, but not beyond, the legal limit, since contract terms requiring law-breaking are generally unenforceable), it's not a valid "out." 

My issue as you may have now understood, is that the third floor REALLY only has one viable entrance/exit to their apartment.

@Benjamin Tarantur, @Lucia Rushton, @Bruce Lynn, @Wale Lawal - Speaking generally, I wish Realtors understood more about seller financing.

Understood the current market and interest rate environment may be difficult to navigate. 

The first agent I talked to was very helpful although not willing to give me access to the MLS which I understood.

Understood that these rules are guidelines, how do you then think about the 1% rule.