How can PHP be used to prevent price-jacking in IPN scripts?

Price-jacking in IPN scripts can be prevented by verifying the price of the product before processing the payment. This can be done by comparing the price received in the IPN request with the actual price stored in the database. If the prices do not match, the transaction should be flagged as suspicious and further action can be taken. 

// Retrieve the product price from the database based on the product ID received in the IPN request
$product_id = $_POST['product_id'];
$actual_price = // retrieve actual price from database;

// Compare the actual price with the price received in the IPN request
if ($_POST['mc_gross'] != $actual_price) {
    // Flag the transaction as suspicious and take appropriate action
    // For example, log the transaction details for review
    // or notify the admin about the discrepancy
} else {
    // Process the payment as usual
}

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