Some are nice, some are trout, some are just a rip-off. Who are your favorite and least favorite NPC merchants?
Personal favorite is the Male Undead Merchant of the glorious Dark Souls. He has an imaginary pet named Yulia and some very interesting madman dialogues. Proof:
One of my least favorite must be the Chinese arms dealer in Deus Ex: Human Revolution. His voice acting was really annoying.
Now you go, multiples are allowed!