It seems like it has the potential to be a decent house hack where I can live in one side and rent out the other side, but I am analyzing it as if I were renting out both units.Here's the overview:Seller accepted my offer of $90,000 (they were originally asking $95,000)Similar sized duplexes rent for around $1,500 total ($750 per unit)The total gross rent would be about 1.6% of the purchase price.I can get a conventional 30 year loan @ 4.5% interest, with a 5% down payment.Mortgage payments with PMI would be around $469 according to mortgagecalculator.org (not including taxes or insurance)Using the 50% rule of thumb to estimate expenses, I might be able to cash flow around $140 per unit.Here's what I found out when I went inside:There are 2 new forced air furnaces.Updated pex and PVC piping.Updated electrical wiring with separate panels.2 old corroded hot water tanks.

I would tell him to read the Model Rules of Professional Conduct as i was walking out his door.  

There are rules on how much you can use, but you get my point.I've heard of agents rolling their commissions into the deal if it's a mutlifamily deal and you are partnering with someone. 

What'd you use as a rule of thumb?

I generally aim for the 1% rule to determine value. 

These rules do come with phase out and exceptions. 

@Jonathan Schwartz I wouldn't necessarily rule it out.  

Would I use the high-level rule of 50% of gross income for expenses and see if mortgage will cover the rest?  

Could you confirm/deny my understanding of these rules?  

If you only buy using the 1% rule that is great and if it is what makes you comfortable, that is great, continue doing it.