If you decide to begin infiltrating this building, the following may occur:
Upon entering the building - a merchant may mention you should leave.
Upon nearing the stairwell in the back, a guard will ask why you're there. Multiple replies are allowed. The 200gp option does allow your party to move on to the 2nd floor without incident.
On the 2nd floor, there is a named NPC that comments on the comings and goings of characters above.
On the 3rd floor, another Guard stops you. 4 options are given. The 4th option relating to Cormyr turns the guard hostile. NPC "Nortuary" also turns hostile. Emissary Tar approaches for dialogue, no matter the situation. He seems to become lost if you do not help him. NPC Merchant remains neutral.
The 4th floor contains a bar, with barkeep and two other NPCs, all of which remain neutral. If you speak to the barkeep, he'll ask where about who you are. The 1st option regarding Sembia keeps the barkeep neutral, but he does not off any services afterward. Destus Gurn approaches you here, can mistake you for Emissary Tar, and you'll be given 3 options. The 3rd option works to make Destus believe you are Tar. The library shelves on this floor contain 6 scrolls as well as many books.
The 5th floor has an immediate dialogue sequence, and all avenues lead to hostility.
NOTE: You will not be able to rest within this building, like most city buildings. Keep potions, spells, and scrolls in mind for dealing with all five floors if you want to do this in one go. It's a long way back (for the lazy like this author)!