def validate_reviews(df):
    """ Enrich no review records with default review scores. """
    
    df['first_review'].fillna(value='1991-01-01', inplace=True)
    df['last_review'].fillna(value='0', inplace=True)
    df['review_scores_rating'].fillna(value=0, inplace=True)
    df['review_scores_accuracy'].fillna(value=0, inplace=True)
    df['review_scores_accuracy'].fillna(value=0, inplace=True)
    df['review_scores_cleanliness'].fillna(value=0, inplace=True)
    df['review_scores_checkin'].fillna(value=0, inplace=True)
    df['review_scores_communication'].fillna(value=0, inplace=True)
    df['review_scores_location'].fillna(value=0, inplace=True)
    df['review_scores_value'].fillna(value=0, inplace=True)

    return df