While I use google reviews more often than other review sites, I know it is a problem. A big chunk of the issues has to do with the whole "local guide" or whatever its called program. People are incentivized to leave reviews anywhere they can because it makes them seem prestigious, so they spam all the restaurants they've not been to or don't care for with negative reviews. This is also a rampant issue for tourist destinations, entertainment locations, local businesses, etc.