aw-shucks, dewy-eyed, green, ingenuous, innocent, naïf(or naif), naive(or naïve), primitive, simple, simpleminded, uncritical, unknowing, unsophisticated, unsuspecting, unsuspicious, unwary, unworldly, wide-eyed

callow, childish, immature, inexperienced, rawchildlike, idealistic, impractical, unrealisticbelieving, credulous, gullible(also gullable), susceptible, trustful, trusting, unguardedbeguiled, duped, gulled, trickedcareless, heedless, thoughtless

cosmopolitan, experienced, knowing, sophisticated, worldly, worldly-wise

critical, cynical, doubting, incredulous, skeptical, suspecting, suspicious, unconvincedcareful, cautious, guarded, leery(also leary), wary, watchfuldown-to-earth, hardheaded, pragmatic(also pragmatical), realistic, soberstreet-smart, streetwise