Since iPhone is indeed a success in the market, a lot of clones and fake unites were being sold with muchcheaper price. Good thing that there was already a video released showing off the big differences that a fake iPhone 6 and the Original iPhone 6 have.
Even at first glance you will be able to determine which one's fake and not. The original iPhone's box have the icons of the home screen of an iPhone while the fake one doesn't have it. The iPhone 6's apple logo is much darker than the fake one's logo. You can also recognize that the lines of the fake iPhone were darker than the original.
These are just some tips for you to avoid buying fake iPhone 6 because even the accessories were very similar and the phone itself were very much a like. So the best way to avoid buying fake iPhones is to buy only at certified apple stores.