Brand New iPhone 6 and Refubrished

I am thinking to Purchase iPhone 6. The problem is that in my country there are no Apple Stores. I need to purchase it through shops who import iPhone's from UK or USA. My friends are telling me that iPhone's that are sold in some shops are Refurbished or opened to replace original parts with duplicate that are similar to original. The cost of an iPhone 6 16GB in my country is around £480 or $750 which is comparatively high than original price on which iPhone are sold in Apple Stores.

I do not want to waste my money on purchasing a refurbished or repaired iPhone. I want to ask that is there any way to detect that the iPhone have been opened or it is refurbished?