Restoration of Treasures

I'm looking for suggestions on reputable sword restoration. So my father has a katana that his grandfather brought home during WW2 and it has been pasted down each generation. My dad was very close to his grandfather and this sword means a lot to him. He is upset that it has deteriated over time and would love to get it restored. The problem is that he is not a expert and is scared that if he took it to be repaired someone would swap out his katana with a look alike. Any help from this community would be greatly appreciated.