Getting a full, locked loan estimate is the only way to truly compare the two. 

(Typically estimate between 2-3% of the loan amount in closing costs: appraisal, credit report, points/origination, underwriting/processing fees, title fees, prepaid taxes and insurance etc)I am sure there are others I am not remembering

Like most wholesalers, they over-estimate their ARV and underestimate their rehab costs.

I have no experience estimating rehab costs and I know costs have drastically changed since books like J Scott's were released. 

You must call Airbnb before you do that, and send proof of repair issues serious enough to require cancellation (photos and repair time estimates) BEFORE you cancel on the guest. 

Stick with the formula, because your ARV isn't necessarily the end buyers ARV and same with repair estimates.

My estimated property value is $1,300,0000.

So they demo part of the house they think needs to be repair and sent over the estimates to the insurance and insurance approved their estimates .

Depending on how accurate you want or need to be a % estimate may not work for you.  

I even provided YouTube links for those tasks of professionals doing them and explaining them in less time than my estimates.