Complete the indicated shop quest to unlock the corresponding bonus.

Seusenhofer Pauldrons and Chest Guards: Complete the Exotica Shop Quest (Blacksmith).
Spada Lunga: Complete the Blood Money Shop Quest (Blacksmith).
Captain's Sword: Complete the Faith Shop Quest (Blacksmith).
Vaticano Treasures Map: Complete the Trendsetting Shop Quest (Art Merchant).
Large Quiver: Complete the Pulling Threads Shop Quest (Tailor).
Fast Poison: Complete the Venomous Shop Quest (Doctor).