Citigroup downgraded Best Buy (NYSE:BBY) to sell from hold, and lowered its target price to $27 from $36.The bank sees increasing competitive threats, limited earnings growth potential, and a lack of positive catalysts.The bank lowered its 2012 EPS estimate to $3.39 from $3.55, vs. the consensus estimate for $3.55 per share, and its 2013 EPS estimate to $3.42 from $3.86, vs. the consensus estimate for $3.78 per share.Best Buy has a potential upside of 39.2% based on a current price of $28.92 and an average consensus analyst price target of $40.25.