What are some common pitfalls when including external shops in PHP websites?

Common pitfalls when including external shops in PHP websites include security vulnerabilities due to unsanitized user input, potential performance issues from loading external scripts, and the risk of relying on third-party services that may change or become unavailable. To mitigate these risks, always validate and sanitize user input, cache external shop data when possible, and have a backup plan in case the external shop goes down.

// Example of sanitizing user input before including external shop script
$user_input = $_GET['user_input'];
$sanitized_input = filter_var($user_input, FILTER_SANITIZE_STRING);
include('https://externalshop.com/script.php?param=' . urlencode($sanitized_input));