Robin Brayman, a 44-year-old Greenfield resident, thought she had saved quite a bit of money buying cigarettes online, until she received a bill from the state demanding more than $2,000 in unpaid sales and cigarette taxes. "I had no idea. When I first started buying, the Web site said the cigarettes were tax-free, duty-free. You assumed you didn't have to pay anything," Brayman said. Brayman, like many other smokers, purchases cigarettes online because they are offered at a deep discount. A carton of Marlboro Full Flavor 100s costs $29.45 plus shipping from BuyCheapCigarettes.com, the site Brayman patronized. The same...