I think gopro have a new model out next year so all the current ones are dropping in price.
Found this company selling official refurb units with a 12 month gopro warranty on: http://www.ebay.co.uk/itm/181878169034
That model has been superceded twice, they done the 4 then the 4 session, I had the 3+ Black, its a great bit of kit, shame they aren’t selling the 4+ Black at that price