Located on the northern side of Oxenfurt is the auction house of Horst Borsodi. In the game, the guards and men of Borsodi are enemies. However, you can get information about the items up for auction in the vault.
The looting in the vault includes currency, gems, viper diagrams, and more. You can also find a painting by an unknown artist that will sell for three times its price.
In addition to the items mentioned above, you can also get new Gwent cards and Witcher Gear by speaking with the associates in the auction house. However, you may get more out of this quest by stealing the items yourself.
For example, the old countess is interested in Witcher gear. She has diagrams for School of the Wolf armor and trousers. She also has some interesting stories about Geralt. You can also find a love letter. You can use the Witcher Sense to read the letters.
The Stranger is also a viable option for an assistant. He will tell you about his plans to “cull” the guards at the auction house. In addition, he will show you a proposition in the basement.
The old countess also has an interesting story. She was once an avid collector of Witcher collectibles. She has a lot of information about Geralt, including her love affair with him when he was young.
In addition to the obvious items, the Stranger also tells you about his plans to recruit a safecracker.