Is buying frequent-flier miles ever a good idea?

Airlines are eager to sell you frequent-flier points and miles. A promotional reward fare could land a flier an economy ticket for 30,000 Flying Blue miles, based on a Monday search. Someone in the second-highest tier of Flying Blue’s subscription plan could acquire that many miles in three months, spending a bit over $400. Air France’s pricing was designed to be more favorable than if a traveler were to buy miles from Flying Blue on a one-off basis, says Peter Schinasi, Flying Blue’s loyalty director for North America. A subscription service like this could allow someone who isn’t a frequent traveler to build up a war chest of miles to enable them to take advantage of deals on award tickets, he says.