Revealing mistake: The glue holding the beard to actor B.D. Wong's (Dr. Hugo Strange) face is always visible.
Revealing mistake: When Harvey Bullock and Jim Gordon enter the apartment of the arsonists, as Bullock approaches the bodies, you can see one of the actor's eyes close, despite the fact he is supposed to dead. (00:20:10)
Answer: "The Merc" was a warehouse like store with aisles that sold mainly weapons, machetes, AK-47s, C-4, barrels of acid, etc. In s02e05, "Scarification", it was shown being raided by GCPD.
Bishop73