My team tore out all the kitchen cabinets, removed the stand up shower, toilet, and vanity, added a laundry closet, knocked out a wall to add a full shower, built a large deck, installed all new flooring, replaced all but one light, had the electric updated and a couple outlets added, repaired two broken windows, replaced some of the plumbing, painted the exterior of the house and all interior rooms, put in all new kitchen cabinets with quartz counter top, all new appliances to include washer dryer and dishwasher, installed a new tub, vanity, toilet, built a stone base to the fireplace, and did some landscaping.

Not completed yet, but we will be replacing windows, and doing a small interior remodel to add a second bedroom What was the outcome?

We're odd in that our project manager actually has a formal degree in Interior Design.

I know when I did interior BPOs it made me very uncomfortable when someone was following me around, trying to talk the subject up.

You might find the property you buy is landlocked and your first job as the new owner is getting legal access.As for access to the interior of the house, if you have a battery powered drill you can get access. 

I have also replaced windows and currently just repainted the interior of the home.

I do architectural drafting and interior design if I can be of assistance to anyone in return.Thanks!

My vacant properties also have interior cameras.

The appraisers I've seen at work always measure the exterior of the finished building, i.e. the outside of the stucco or brick...Maybe someone else measured the interior rooms as @Chris Seveney said, and now you have 2 numbers floating around.It actually could be in your favor if you can get the seller to use the same square footage number and apply it to the smaller SF.... :-)

Here are some other facets of a rehab which may be more expensive, roofing, windows, HVAC. electric service exterior and interior.