naive and trusting
ingenuous - naive
If somebody is described as ‘ingenuous’, they are considered to be lacking in worldliness or sophistication. It is characterized by a kind of child-like innocence and openness which can be both charming and dangerously naive. Not to be confused with ‘ingenious', which means 'clever or skillful'.
Tom didn’t leave the business for a new challenge, he left for a bigger paycheck. It would be ingenuous to think otherwise.
Claire has an ingenuous smile that is very disarming, but she is no push-over.
The ingenuousness of asking a total stranger for a lift is incredible to me. Anna needs to be more careful.