Almost all mehadrin restaurants here in Israel have websites and customer reviews. Most customers give good or excellent reviews , not all. The owner provides this website and is most interested in all reviews. The good ones that develop his clientele, and the bad ones so he can improve his product and service. This system is universally accepted and used, and loshon hara in this system has never been an issue. Yes. the halachah is always the halachah, period. This system, agreed upon and accepted by all, does not contravene any halachah. But incorrect interpretations of the halachah of loshon hara can damage both the consumer and provider, and that would be against halachah , and more than one at that.
Shabbat Shalom from Eretz Hakodesh