The most common type of clear coat finish on modern pianos is not shellac, lacquer, or polyurethane. It is high-gloss polyester, which yields a beautiful, almost mirror-like level of gloss. Virtually all ebony (black) finishes in recent years are coated with polyester, as well as many other colors.
One of the greatest advantages of polyester is its durability – it is very resistant to scratches, wear, and chemical damage. However, for the same reasons, it is also difficult to repair when it does get damaged. These pictures are of a piano I worked on recently that had received very heavy use in a school environment for years. Even this major damage, however, can usually be repaired to an almost like-new finish. The biggest hindrance is typically cost, as it is labor-intensive to repair polyester, and the finish materials needed are specialized and somewhat expensive as well.
If you have a piano with finish damage, just ask for an estimate! I do polyester finish repair at an adjusted hourly rate which includes materials cost. Many common finish repairs can be accomplished in-home.