The principle of privity of contract dictates that only parties to the contract have rights and obligations under it. In this scenario, John is the party to the contract with the shopkeeper, not Emily. Therefore, Emily has no contractual rights to demand a replacement or refund directly from the shopkeeper. Instead, John, who is the contracting party, must assert his rights under the contract for a remedy. 

Key Point: This question highlights the principle of privity of contract, which is fundamental in contract law. It emphasizes that only those who are parties to a contract can enforce its terms or seek remedies for breach, an essential concept for understanding contractual rights and obligations.