Apple opened the iPhone Duo pre-orders about four days ago and seconds after the shipping dates slipped into January next year. With every product in extremely high demand and low on stock, scalpers gather and try to buy the item in large quantities and then sell it at an inflated price. That's why Apple now imposes a limit of two iPhone Duos per customer. The limit has so far been confirmed in the US, UK, Japan and Spain, but it's likely worldwide.There are already some eBay listings selling the iPhone Duo at an eye-watering $5,000.This is not the first time Apple is trying...