Groupon offers its first car coupon deals as the firm looks to expand into bigger-ticket items....

Groupon offers its first car coupon deals as the firm looks to expand into bigger-ticket items. Critics say the offer is problematic, as it locks consumers into a deal with one car dealer, giving away a consumer's ability to shop the market. Rivals Amazon (AMZN +2.4%) and Google (GOOG +1.1%) stand ready to undercut Groupon's market share with new products.