This is a causal detail question asking for the specific reason behind a character's criticism. The phrase "According to the passage... primarily because" signals straightforward cause-finding in the text. Locate where Elias criticizes Mr. Thornton: "Mr. Thornton is a grocer who thinks he is an engineer." The criticism is that Thornton lacks the expertise to make technical suggestions about clock repair—he's overstepping his knowledge. This is emphasized when Elias rejects Thornton's idea about replacing brass with modern alloy, arguing Thornton doesn't understand that this would "alter its soul." Wrong answers might suggest cost concerns, doubting the shop's ability, or being too demanding—but the text explicitly frames the criticism as about Thornton's lack of clockmaking expertise making him unqualified to suggest modifications. Pro tip: For "primarily because" questions, find the character's actual words explaining their view—don't infer complex motivations when simple, stated ones exist!