Green’s Dictionary of Slang

(US black) a local gossip, who ‘preaches’ only to those who idle away their days outside the general store of some small town; thus storefront preaching n.

1959		C. Himes Crazy Kill 17: Why do you let that store-front preacher run your business, Aunt Mamie.
1961		C. Himes Pinktoes (1989) 188: A number of store-front preachers did a discreet business in teaching white ladies how to follow the rhythms of the Georgia Grind [etc.].
1972		The Temptations ‘Papa Was a Rolling Stone’ 🎵 Papa doing some storefront preaching / Talking ’bout saving souls and all the time leeching.
1982		Dly News (NY) 21 Nov. 7/2: A former storefront preacher estimates that two or three storefronts open in the city every week.
1992		Tampa Trib. (FL) 3 June 10/1: Like the Los Angeles police and looters, we are blind. Storefront preacher, let us see.