Either they did not do their homework right (appraisal comes in lower than their estimate, insurance/taxes are higher than their estimate, property did not have clear title, and/or the property has deferred maintenance) or they are shopping without having any experience in the industry. 

As long as the appraisal will support it, you can get it refinanced.

Outside of appraisal and title they keep control of the entire process; processing,underwriting, closing and funding 

Will the property pass appraisal and inspections, and will I get funded at closing?

Or that my ARV or the appraisal is waaaaayyyy off...

Shouldn't be the top concern, and cabin/tiny homes can be superior investments, but something to consider Also, building on this point, it may be more difficult to get financing if the property appraises as "rural."

But, the appraisal will have to consider the current use.

Begin your 'pre qualification' process for the acquisition now (most commercial lenders won't issue a PreQual but rather a LOI) In general, Commercial transactions can take longer due to extended due diligence, appraisal, environmental reports and financing (60+ days) so you'll want to initiate your search during the marketing of the down leg as it can cause a tighter timeline than a residential transaction. 

For the first loan the bank has to take the "Niederstwertprinzip" in account, that means, even if you buy at a huge discount, the bank can not appraise the property higher than your purchase price for that loan.

Box A is direct lender charges, box B are things the lender is making you get that you cannot shop for (for instance, the appraisal or credit report), and box C is closing costs that you can shop/control- Lenders can move things around between boxes A and B to change the way costs appear.