How can the user ensure that the data sent through the form is properly handled in the PHP script?

To ensure that the data sent through the form is properly handled in the PHP script, the user should sanitize and validate the input data to prevent security vulnerabilities such as SQL injection or cross-site scripting attacks. This can be done using functions like htmlspecialchars() to prevent XSS attacks and prepared statements to prevent SQL injection attacks. Additionally, input validation functions like filter_var() can be used to ensure that the data meets the expected format.

// Sanitize and validate form data
$name = htmlspecialchars($_POST['name']);
$email = filter_var($_POST['email'], FILTER_VALIDATE_EMAIL);
$message = htmlspecialchars($_POST['message']);

// Use prepared statements to prevent SQL injection
$stmt = $pdo->prepare("INSERT INTO messages (name, email, message) VALUES (:name, :email, :message)");
$stmt->execute(array(':name' => $name, ':email' => $email, ':message' => $message));