ATTENTION holiday shoppers, here is your annual public service announcement: The overwhelming majority of Black Friday deals are duds.

We all know the drill by now. Retailers’ sales promotions begin weeks before Thanksgiving, with a smattering of modest deals that eventually build up to the shopping bonanza that is Black Friday — the day after Thanksgiving. That is followed by Cyber Monday, a so-called online shopping extravaganza that takes place the Monday after Thanksgiving weekend.

To whet shoppers’ appetites further, it has become increasingly fashionable for online retailers to build up anticipation for Black Friday with so-called flash deals. These last only a few hours, putting pressure on consumers to make purchases with little or no research.

Yet however you shop, the chances of snatching a great deal for a quality item are slim, largely because Black Friday is mainly designed for retailers to clear out unwanted goods, and because best-selling products rarely drop much in price. So we teamed up again with The Wirecutter, a website for product recommendations that was recently acquired by The New York Times, to weed out the good deals from the bad.