The Poison Salesman is involved late in the Murder Mystery quest. At a certain point, the player will travel to Seers' Village pub and ask him about the poison that was used in the murder. He is not very helpful, however, and tells the player that all the party guests purchased poison from him.
The Fremennik Trials
During Manni the Reveller's trial, the player will be required to visit the Poison Salesman and purchase a keg of low-alcohol beer for 250 coins.
Dialogue
This article on an NPC has an associated dialogue page. Click here for a transcript of possible conversations with this NPC. Click here for a list of other transcripts that this NPC speaks in.
Trivia
In dialogue, the poison salesman frequently advertises a concoction he exclusively manufactures, which he calls "Peter Potter's Patented Multipurpose poison". This would imply that the poison salesman's name is Peter Potter.
His name may be a reference to the Peter Rabbit books written by Beatrix Potter. While there is little that thematically links the poison salesman to the franchise, his proximity to McGrubor's Wood – which is a likely reference to McGregor's garden – may hint at the influence.
Kandarin✓
