Every city has it's own merchant. This is the only person who will buy sellable quest items from players. The city merchant is funded by the city so each time an item is sold, the money comes directly from the city coffers.

The merchants for each city are located:

City	Merchant	Description	Location
Mercinae	merchant293	a stern faced merchant	Inside a small shop
Parrius	merchant298	a stern faced merchant	Inside the Parrian Shop
Springdale	merchant35154	a stern faced merchant	Springdale grain repositories
Thakria	merchant296	a stern faced merchant	Dalgar's Pawnbroker