Will the black spots sand out? What will it look like if they don't?

Many times when carpet is removed to expose hardwood flooring below, evidence of pets stains or other damage are revealed. Unfortunately, these stains do not usually sand out. This is because the pet stain stays wet in the carpet pad and permeates the entire depth of the lumber. Pigmented stains may help mute the appearance but not always. Moreover, the chemicals in in these stains may react with our finishes causing adhesion problems. In these cases, the only way to have a spot free floor is to replace boards before sanding takes place. When deciding whether to have repairs done to your floor, keep in mind that once the floor is sanded, spots and flaws usually stand out more because the rest of the floor looks notably newer.

Photos of stains that didn’t sand out and the repair process