Well that's a complete lie, aside from being bad advice in the first place. I'm not a house appraiser myself however I am the accomplice of many flipped houses, and I would say generally the most important thing is appearance. People want a house to looks like it's ready to move into without them having to do anything.

Some of the most cost effective things you can do (if you do the work yourself) is just painting and cleaning as they make such a difference in this regard. 2 other parts of the house that benefit from this is the kitchen and the bathroom. Most other rooms are "decided" by the new owner with the main selling points being size and floorplan (ie things you can't change easily), but alot of things in a kitchen and bath will be used as is at least temporarily (ie appliances, countertop, vanity, toilet, etc.) I find it's pretty hard to not get at least your investment back when making improvements on these two rooms so long as your not being dumb.

Aside from that your house is mostly just appraised on age, size, location. Usually to get an idea, we would look at another house that sold in the same area, find it's price/sqft, multiply that number and our sqft, and then decide how much to go up/down based on the differences between our house and the house that sold. Good luck~~~