[mothered]

But surely they will have another of said cheap phone to hand to weigh.. I mean they will surely weigh those in an investigation.. or do you think they will only weigh the one you sent back.. also what's to say they dont go through the contents and check.. and if they see the extra item in there they will probs call the police with good evidence against me lol

I don't think you've grasped the concept of the sealed box method.

The objective, Is to replace the original Item with anything of the same weight and seal It perfectly as per the manufacturer's packing without any signs of Inconsistencies whatsoever. As such, when you return It, they'll assume It hasn't been opened, then scan It and place It back In their Inventory.

A refund/replacement will be Issued thereafter.