@BrandedAX @BozMagic @blablablub To understand what's going on and why the customer is critical of Shuu's repair you should know that the Japanese have a special artform for repairing broken things called Kintsugi/Kintsukuroi that is usually applied to pottery.
https://en.wikipedia.org/wiki/Kintsugi
In fact, when broken pottery is repaired by an artisan, it is always expected that the artisan would apply this technique. It's the traditional understanding of what an artisan's repair would look like, as opposed to a professional restorer's work. In the Japanese sensibility a restored object is an object that has lost part of its value from being broken. That's why "proper" repair should instead seek to increase the value of the repaired object. That's the reason to bring the damaged object to an artisan instead of a restorer. The characters in this manga also understood it the same way. That's why Shuu was in such a deep rut in the previous chapter (and this one), because he knew he had no idea of how to do what was expected of him. He could repair the object, but he doesn't have the skills necessary to improve the object on repairing it, as a traditional Japanese artisan is expected to do.
Mokume-gane, the artform that Shuu's dad was studying, is in essence a method of inserting layers of different metals to create a wood-grain pattern.
https://en.wikipedia.org/wiki/Mokume-gane
However, in the context of this conversation, it could also be used as a repair method for a damaged metal object. So, given the traditional understanding of what it means to have an artisan repair an object and the customer's knowledge of what Shuu's dad was pursuing, the request for repair was always meant to be interpreted as "make it better with your technique", not to simply return it to its original state. In essence the customer's expectation was to have Shuu try using mokume-gane as a form of kintsugi. I agree that this is a rather unreasonable expectation for him to have, but the basis for his expectation is perfectly rational within the context of Japanese art culture. It's something Shuu's dad or other skilled artisans of his level could and may very well have done.