if you do not talk about a person,you talk about the public you say למשל the kashrus in bnei Brak is very weak,you did not say which store and which restaurant you are referring to, there are hundreds of restaurants and stores in bnei Brak?
or you say the mezuzah coming from England are not the best,everybody understands there are a lot of stores in England ,is that מותר to say? IN A CASE THAT THERE IS NO תועלת ?
If you talk about the public, that could be even worse lashon hora because you are now slandering the public. If everyone knows that there are a lot of good restaurants, and good mezuzas, why are you saying it in a way that sounds like they are all that way? If however you say it in a way that sounds like it is only about a specific one, and that the rest or most of them are fine, then it is not considered lashon hora.
Chofetz Chaim Hilchos Lashon Hora 10-12, see footnote 61in Dirshu Edition.