// get the cart data from the POST
$data = hikaInput::get()->get('checkout', array(), 'array');
// check that the products quantities are there
if(empty($data['cart']))
return true;
if(empty($data['cart']['item']))
return false;
// get the cart from the database
$checkoutHelper = hikashopCheckoutHelper::get();
$cart = $checkoutHelper->getCart();
// compare the quantities from the POST in $data['cart']['item'] and the quantities in the cart in $cart->products
// if they are the same, the cart has not ben changed and thus you can redirect
// if they are not the same, and the products requiring the verification are being removed, you want to let the process continue
// if they are not the same, and the products requiring the verification are not being removed, you want to let the process continue so that the change can be taken into account, add a flag, and implement onAfterCartSave where you can then do the redirection if the flag is present