Unless I'm totally missing something that seems like a way to get around the hassle and headache of relying totally on the accuracy of your ARV (not to mention the bank/appraisers willingness to match that when the time does come to refi) concerning the BRRRR method.

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There are simply too many unknown variables about a property to refine your numbers to 100% accuracy but the more you know about a property, the better your "Guesses" are going to be.As you noted, the down payment requirements on even Small Commercial buildings (< 1MM) are still hefty.

I have to compile it myself for accuracy.

Sometimes if people do not like the evaluation then they can try and stiff the appraiser with paying for it.With an appraisal for a bank, construction loan,etc. the appraiser has standards to meet and can be held more accountable so those reports tend to hold more weight on accuracy although an appraisal is just an opinion and not an absolute.No legal advice given.    

Do they check for accuracy when you send them your tax returns and bank statements?

The only numbers I would know with any reasonable accuracy are costs for utilities/phone/cable, insurance, property taxes, HOA fees, and mortgage payments.I suppose the best way to do it is to start requesting information from the listing agent and the condo association for each of the properties we are looking at, but I'm so used to being able to do my own analysis on properties before reaching out to anyone. 

We have great success with around a 95% accuracy rate at a price well under .80 per hit depending on your monthly volume.   

I think this information is helpful for me to estimate potential deals with more accuracy. 

I would never rely on Zillow's 'Zestimates' of property value as there are too many data points they don't have access to, and also the market is fickle, so no company can track prices with 100% accuracy.