Concerns are growing about the authenticity of online ratings. People making comments often don’t give their full or real names; others don’t disclose their relationship with the business they’re reviewing. That can allow business owners to pad their scores with rosy testimonials from friends, family, even themselves. Some pay so-called review mills to churn out positive statements. Others have trashed rivals with negative comments. As many as 4 out of 10 online reviews are phony or biased in some way, said Bing Liu, a computer science professor at the University of Illinois in Chicago who develops software to detect fake reviews. Liu said the challenge for Yelp and other review sites is in keeping pace with the latest tactics. “It’s going to be a problem forever because the incentive is too high,” he said.