That's criminal law this is a civil issue. When two parties disagree on a civil issue, the court is required to find in favour of one of them, so the case is decided on the balance of probabilities, and neither party gets an assumption of either 'innocence' or 'guilt'.
Technically there is a contract the contract of purchase which occurred whenever the phone was bought. Under the law of England & Wales, contracts aren't just paper documents, they're (roughly) any agreement that is intended to be binding under law which is defined so that each party does something to their detriment. In this case one party lost possession of money and the other lost possession of a product, so that's a contract.
The Sale of Goods Act implies terms into that contract that the item bought must be suitable for the purpose for which they are commonly sold (per s14(2b)), i.e. in this case it must be possible to charge and activate the thing. The only issue might be with section 35...
Section 35 covers acts that a purchaser can do which make it clear that they have accepted the goods in their current state. One of the ways they can do that is to do "any act in relation to them which is inconsistent with the ownership of the seller." Having the phone around a showroom and otherwise treating it as your own property is inconsistent with the phone still being the property of Apple. It doesn't matter if the buyer hasn't actually examined the goods, provided they've had a reasonable opportunity to do so, which per caselaw (Bernstein v Pamson Motors, though it refers to an older version of the Act for which I don't have the text) includes an evaluation of the amount of time the retailer can be expected to keep a commercial ledger open for.
Basically, they want to balance the rights of the retailer and the consumer. It isn't fair to think that a consumer should be able to walk back into a shop just less than 6 years (which is the limit for contract disputes per the Limitation Act) after they bought a product, having only just inspected it, and expect the retailer to replace it. But similarly it isn't fair to say something like "consumers must inspect all goods within 2 weeks". I think the 6 month figure quoted elsewhere on this thread is likely to be a combined interpretation of various bits of caselaw rather than a hard and fast limit.
In any case, I think the practical advice offered elsewhere on the thread is correct. Remind them of their duties under the Sale of Goods Act and they're unlikely to see any benefit in pursuing the issue in court, especially as it prima facie appears to reveal a latent defect in their design and they're unlikely to want that publicity.
Important disclaimer: I am not a legal practitioner. I don't work in a legal field. My interpretation of the statute and caselaw may not be accurate and should not be relied upon.
