Auto dealers have long been willing to take an old clunker off a potential buyer’s hands in order to clinch a sale of a shiny new model. Now airplane makers are following suit. Boeing (BA) is acquiring previous versions of the 747 from airlines ordering its new, tough-to-sell 747-8. Of the 19 older 747s that have changed hands so far this year, Boeing has snapped up seven, according to data compiled by Ascend Online Fleets. That makes it the biggest buyer of the used jets in 2013.