The two-way mirror in this episode would be ineffective with Frasier (Kelsey Grammer) and Roz (Peri Gilpin) in a room with the lights on. Two-way mirrors only work when the viewer's room is dark. In other words, as shown, each side would be equally visible to the other.
The survey monitor in the booth with Frasier and Roz reads off the bio on the dissenting panel member of the focus group, including his name. For security reasons this would never happen in real surveys. By the end of the story the wisdom of this policy becomes very evident.
As Frasier (Kelsey Grammer) and Niles (David Hyde Pierce) walk from the kitchen musing about a focus group expressing an opinion about Freud, the camera takes such a wide shot that you can actually see the stage lights above the set.
Pate de fois gras is made from goose liver. Niles (who should know better) says it is duck liver.
Frasier ridicules focus groups to Niles by comparing them to Viennese laborers giving their opinion of Freud's theories of the Oedipal Complex and Penis Envy. As an experienced debater he should know that he is committing what's called a "Red Herring" argument. His focus group was there for their opinions of his radio show, not psychological theories.