The Witcher 3 merchants

Merchants in the The Witcher 3: Wild Hunt can buy and sell: food and drinks, all alchemical ingredients, and junk items. Other (junk) items can be sold to merchants at higher prices compared to other types of shopkeepers, except keys and currencies. They also generally play gwent.

White Orchard region

 * Bram
 * Merchant (White Orchard sawmill)

Velen region

 * Anselm
 * Merchant (Blackbough, card player)
 * Merchant (Blackbough, cart)
 * Merchant (Boatmakers' Hut)
 * Merchant (Border Post)
 * Merchant (Calveit Watchtower)
 * Merchant (Claywich)
 * Merchant (Downwarren)
 * Merchant (Lindenvale)
 * Merchant (Midcopse)
 * Quartermaster (Crow's Perch)
 * Trader (Crow's Perch)
 * Trader (Oreton)
 * Travelling trader (Velen)
 * 3 Merchants outside the Nilfgaardian Army Group 'Center' Camp
 * Tavar Eggebracht

Other Merchants

 * Merchant in the liberated camp west of Lurtch
 * Merchant at the crossroads between Mulbrydale and Devil's Pit

Novigrad region

 * Merchant at Aeramas' Shop in Gildorf
 * Merchant in Putrid Grove
 * Merchant in Hierarch Square
 * Helmut Altberg in Hierarch Square (also labelled "Merchant")
 * Merchant in the Fish Market
 * Marcus T.K. Hodgson, just off Hierarch Square
 * Loan Shark, in The Bits between the Southern and Oxenfurt Gates
 * Merchant by the docks in north Silverton
 * Merchant who sells fish in Silverton
 * Merchant in Mohrin Village (only with "Hearts of Stone" expansion)
 * Ofieri merchant in Upper Mill (only with "Hearts of Stone" expansion)
 * Merchant at the circus troupe encampment northwest of Carsten (only with "Hearts of Stone" expansion)
 * Merchant in Stacheier (only with "Hearts of Stone" expansion)
 * Merchant at Crane Cape (only with "Hearts of Stone" expansion)

Other Merchants

 * Scoia'tael Merchant in the forest outside Novigrad
 * Merchant outside the city walls near Farcorners

Ard Skellig

 * Merchant in Blandare
 * Merchant in Fayrlund
 * Merchant in Fyresdal
 * Merchant in Holmstein's Port
 * Merchant in Kaer Trolde harbor
 * Merchant at the Sawmill
 * Sjusta
 * Merchant at the Lumberjack camp south of Sund
 * several travelling merchants and traders

Hindarsfjall

 * Merchant at the Isolated Hut
 * Merchant in Larvik

Spikeroog

 * Merchant in Svorlag

Faroe

 * Merchant in Harviken

Toussaint region

 * Butcher
 * Clerk at Villa Vedette
 * Hugo
 * Merchant at Dupont & Sons
 * Merchant in Flovive
 * Merchant in Francollarts
 * Merchant at the Perfumery
 * Merchant at The Cockatrice Inn
 * Merchant at the Wine Market
 * Pierre

Land of a Thousand Fables

 * Little Flint Girl