Before you buy an apartment, you should inspect it very carefully. And here there are no minutiae. The most dangerous thing is not to miss hidden defects of the apartment. For example, the stains on the wallpaper may not be an old leak, but a fungus, and therefore the cost of repairing the defect will be many times greater than if you have flooded. A carpet on the wall (if the apartment is located at the end of the house) can serve not as a decoration of the house, but as camouflage for a freezing wall. If the apartment is located on the top floor, it does not hurt to ask about the condition of the roof and the technical floor, if any.