Unsur­pris­ingly, this brief analy­sis of how reviews influ­ence sales on Ama­zon equates quite well with my pur­chas­ing behav­iour; I wouldn’t feel com­fort­able buy­ing a prod­uct with 100% pos­i­tive reviews unless I knew per­son­ally that it was awe­some. And a prod­uct with less than 15 reviews or so? For­get about it.

[A] hand­ful of bad reviews, it seems, are worth hav­ing. “No one trusts all pos­i­tive reviews,” [John McA­teer, Google’s retail indus­try direc­tor,] says. So a small pro­por­tion of neg­a­tive comments—“just enough to acknowl­edge that the prod­uct couldn’t be perfect”—can actu­ally make an item more attrac­tive to prospec­tive buyers.

The sheer vol­ume of reviews makes far more dif­fer­ence, accord­ing to Google’s analy­sis of clicks and sales refer­rals. “Sin­gle dig­its didn’t seem to move the nee­dle at all,” says Mr McA­teer. “It wasn’t enough to get peo­ple com­fort­able with mak­ing that pur­chase deci­sion.” But after about 20 reviews of a prod­uct are posted, “We start to see more reviews—it starts to accelerate.”