Not only are people willing to pay more than RRP just insane but they're also stupid. I bet most of the people selling those phones on there are those who have taken an early upgrade, so rather than drop their tariff to SIM only, they just carry on paying the normal price and sell the phone to get a lump sum. I'd never pay more than RRP for anything and I certainly wouldn't want to open myself up to the possibility of owning a brick if the person responsible for the contract stops paying it. But people just don't think like that and if they want to take the gamble then fair play to them.