In this example, these two used iPads are identical, but one got its owner an additional $100 when he was ready to upgrade. The first iPad owner sold his device on a popular electronics buy-back site like Gazelle. He got $140 and the money was in his hand in three to five days.
Meanwhile, the second iPad owner had signed up for eBay's My Gadgets and saw that similar devices had recently sold at auction for around $240. My Gadgets then made it easy to setup his own auction, even allowing him to print out a shipping label (paid for by the buyer) once his iPad sold. It took about two weeks, but soon he had a whopping $240 in his hand.
So, before simply trading in your old electronics, take a look at eBay's My Gadgets to see what they're really worth, because doubling the value of your trade-in could cut your upgrade costs in half.