High gloss polyester finishes such as those found on Yamaha pianos, as well as many European and Asian instruments, can be made to look almost perfect. That perfection makes an accidental scratch or chip quite upsetting. Trying to fix high gloss polyester with normal finish repair materials and techniques, no matter how good the technician is, will never be satisfactory.
Even if the repair looks acceptable when finished, it will likely degenerate within weeks or months because the repair materials will not respond to environmental changes the same way as the original finish materials react. Christopher Lech has mastered the technique of polyester repair on pianos such as Yamaha which have a high gloss finish.