The Rosetta Stone had only recently been found; Egyptology was nascent in 1835 — giving Smith apparent cover

Mike points out that in 1835 the Rosetta Stone had only recently been discovered (found in Egypt, then studied in France), and knowledge of how to read Egyptian hieroglyphs was barely emerging in Europe. This meant almost no one in America could verify whether Smith was accurately translating Egyptian. This context explains why his contemporaries might have believed his claims.