On his way from Philadelphia to the Jersey Shore for some senior-week revelry in the early ’80s, 17-year-old Gary Barbera had business on his mind. He had seen a newspaper advertisement for a 1971 Chevy Nova and decided to buy it  not for cruising with his buddies but as an investment. Later that week, after giving the Nova a good wash and some detailing, he sold his very first car, at a profit of $360.

Two years later, the 19-year-old was running a Buick dealership. In his mid-20s, he says, he became the youngest Chrysler dealer in the country. His success continued, and he was consistently named a top-rated dealer in the mid-Atlantic region with annual sales that exceeded $100 million. He later added a General Motors dealership. His aggressive advertising  including a 2009 commercial that featured a President Obama look-alike offering cash for clunkers  helped make him a household name in Philadelphia.

But his small-business success story took a dark turn in 2007, when the Internal Revenue Service began an investigation of Mr. Barbera’s financial practices. The inquiry revealed $77,675 in unpaid taxes, mostly on a number of Chrysler “dealer reward” bonus checks issued in his name. The I.R.S. concluded that Mr. Barbera had been deliberately “skimming” income to avoid paying taxes and filed charges.

Now 46, Mr. Barbera recently pleaded guilty to one felony count of filing false tax returns. He was ordered to pay $119,744.55 in restitution and interest plus a $30,000 fine and is serving three years’ probation. Under house arrest, he wears an ankle bracelet but can go to work to run his Philadelphia dealership.