@DJDarren it certainly does them no harm in that respect. But the prices they offer for trade-in are so low, that if the current owner wanted to sell it on, they'd easily get more money taking it a few doors along to any second hand electronics shop. More it reduces the amount of spare/backup devices buyers have to rely on. Buy a phone 2 years ago, trade it in today for a new model, and when you break this one next week, you've no longer got a spare to limp along with while considering options.