Miami's franchise of the Play It Again chain has had four years to turn into a sprawling, sterile, time-wasting white elephant (as chain stores are wont to do). It hasn't. The service is friendly and efficient without being cloying or annoying; this is especially important at a place that buys and sells new and used gear. Among its wares are all kinds of balls, weights, togs, racquets, clubs, and bats. You can scoop up used tennis balls for two bits apiece, find junior titanium drivers for about $20, and even try out an array of putters on the carpeted showroom floor, where an automatic ball return is set up. The congenial staff will restring your racquet, relace your glove, or regrip your clubs. With a more comprehensive inventory, tighter restrictions on trades and consignments, and a few thousand more square feet of space, Play It Again could easily become The Sports Authority. Here's betting (and hoping) that never happens.