The achievement says to "Listen to all of the Blacksmith's conversations."
Because some of these are missable, I'd like to know when Haedrig's conversations first become available and if and when they become unavailable. The Weary Blacksmith seems particularly missable.
Best Answer
Because some of these are only available after the Blacksmith has been unlocked during A Shattered Crown in act I, you will have to start already completed quests after having unlocked the Blacksmith.
The town becomes inaccessible after you start the objective Find Diablo during The Prime Evil in Act IV and so any not heard by that point have been entirely missed.
Act I
Act II
Act III
Act IV