Magic Town (1947)

Rip Smith's opinion-poll business is a failure...until he discovers that the small town of Grandview is statistically identical to the entire country. He and his assistants go there to run polls cheaply and easily, in total secrecy (it would be fatal to let the townsfolk get self-conscious). And of course, civic crusader Mary Peterman must be kept from changing things too much. But romantic involvement with Mary complicates life for Rip; then suddenly everything changes.