In the novel Silas Marner, George Elliot ensures that the reader gets the entire picture together of the description of a typical small town, isolated from society, and that each and everyone of its inhabitants is as picturesque and has an interesting set of characteristics that would reflect the bucolic aspect of the story.
In this case, Mr. Snell was the town's "investigator", but not in a derogatory way. He is the typical small town guy who He served many roles in Raveloe: Inn keeper, deputy constable, and town's problem solver. He is smart enough to have a clairvoyance (as it is described in the story) to visualize things and uses his strong intuitive powers to, like the story says "put two and two together".
In discussions, he is the no-nonsense man. He will put the facts together, organize them, categorize them, classify them, and analyze them with precision to get to the point. He is the one who adds all the clues and connects all the dots when gossip, myth, legends, or happenings come up in conversation. He is the town's reality checker.