I've never heard or read of anyone, not a single person, complain that Brixton market has become gentrified though. In fact quite the opposite - it's become more run down and lost some of its best stalls in recent years. There have often been people of these boards wanting 'posher' stalls, not a host of people talking about how they can't buy an orange because all the stallholders have started selling pashminas and artisan french cheeses.
For someone who's claiming that the gentrification of Brixton market is 'obvious,' you're presenting a very weak case. Picking on one stall in essence and talking about pubs that are barely near to the market area - whatever the Atlantic might have been, I certainly wouldn't have called it the market traders' favoured local.
Anyone would think you're trying to force another pointless argument. Nearly everyone would concede that Brixton is showing signs of gentrification, but the market's a different matter. Sadly it's looking left behind and in decline, not ponced up and different in (class) direction as you seem to be suggesting.