He confirmed my assumption that the estimates on Zillow, etc. are pretty much junk, that they will regularly be at a minimum 5% off, sometimes much more, and that what he has seen in the past is that new investors have based their numbers (purchase price, rehab budget, etc.) on these inaccurate numbers and what started off looking like a great deal, turned out to be a bad deal for them after the actual comps,  inspection, and assessments. 

I've tried and spent a crazy number of hours doing research on taxes and assumptions, but it's such a big financial decision that we don't feel comfortable navigating it on our own.

Assumptions for VA and FHA are full documentation- w-2, 1099, IRS taxes, paystubs, bank statements... the War and Peace novel.

The client cup of tea is loan assumptions with value add.

Which is why the BRRRR Method or Sub To or Assumptions or all of these other strategies are important. 

With the assumption your FICO score is around 760. 

My assumption is that all tenants have an interest in keeping their cards close.

I've made the mistake in the past of going by self-imposed assumptions but a lot of times they turned out to be false.

You can add them subtract them use conditional logic.. truly fascinating and a POWERFUL tool to master.Imagine you are in a city, and one investor is in that city, and the rest are homeowners.Let's make an assumption that DMM actually works (it truly doesn't, but let's assume it does).If one investor sends everyone mailers, great!

@Sehyun Lim Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.So, when investing in areas they don’t really know, investors should research the different property Class submarkets.