The achievement says to "Listen to all of the towns merchants conversations." Where are all these merchants located and are there any criteria to start the conversation (e.g. quests etc)?
To get credit for each "conversation", you simply have to walk close enough to the NPC to trigger their dialogue.
- Arghus the Collector - On the path behind the inn, near where the Mayor's cart was stuck.
- Radek the Fence - on the path behind the inn at the fork between the boats and the Weeping Hollows.
- Bron the Barkeep - In the inn near the entrance to Leah's room.
- Tashun the Miner - Near Cain's house and the Healer.
- Tilnan the Collector - In the Bazaar against the northwest wall near the bridge.
- Silmak the Fence - In the Hidden Camp in the small northwest alcove, near the Healer.
- Sadeir the Innkeeper - In the Bazaar's inn in the north corner.
- Lugo the Miner - In the Bazaar to the right of the inn's entrance.
- Squirt the Peddler - In the Bazaar by the fountain near the bridge.
- Vidar the Collector - Far southern corner.
- Litton the Fence - Far western corner.
- Gorrel the Quartermaster - Far eastern corner.
- Botulph the Miner - Southeastern corner, between Gorrel and Vidar.
(taken straight from d3db.com)