What do YOU think is fair? Keep in mind that you are trading in a used iPhone 6 Plus an iPhone 6 that may or may not be used. If you really want to get rid of it and get an iPhone 6 then go ahead and either sell it and then take that money to buy the iPhone 6 or do an even swap or something. Remember, all that matters is what is fair and acceptable to YOU. With that in mind, if you're going to try to sell or trade your device here at iMore, go to the Marketplace section, read the rules carefully, and then create your WTS/WTT thread in the same section. Thanks.