GiffGaff selling old moile

isabellac

Do you have a GAME shop near you? I know several people who have traded in with them and received a very competitive price for their phones (in cash, or higher in store credit if you actually needed to buy something from them). Probably nicer than doing it online as they will do their diagnostic bit then and there to generate your quote. If you have a look on their site you should be able to get an idea of the kinds of prices you might be offered depending on the condition of your 6s, the storage size, whether it's locked to a network, etc.

Pro tip - if your handset is locked to your previous network, give them a call and see if you can get it unlocked to try and maximise your trade-in price. The unlocking process will take up to 10 days as they have to submit to Apple - dependent on your network this could be free or under a tenner (o2/EE) or up to about 20 quid (Vodafone).