The LaFontaine Automotive Group has become the first in the U.S. to offer a Groupon car voucher deal, reports Crain’s Detroit Business. Its Highland, Mich., dealership, LaFontaine Buick GMC Cadillac, completed 2010 as the nation’s top seller of all three vehicle makes. A Groupon discount is expected to boost sales considerably. Groupon: From facials to Read on! →