function update_payment_options() {
    // select valid payment options according to customer type
    var subListArray = [];
	subListArray[0] = 'Select a type please';
	subListArray[1] = ['ca|Cash','cr|Credit','pp|PayPal'];
	subListArray[2] = ['sh|Shop','mt|marketTrader'];
    var pay = document.getElementById('paytype');
    var payment = document.getElementById('customerType').selectedIndex;
    pay.options.length = 0;

    if(payment == 0){
        for(var i = 0; i < pay.options.length; i++) {
            var option_element = document.createElement('option');
            option_element.value = "";
            option_element.textContent = subListArray[i].split("|")[1];
            pay.appendChild(option_element);
    	}
    }


    else if(payment == 1) {
    	for(var i = 0; i < pay.options.length; i++) {
            var option_element = document.createElement('option');
            option_element.value = "";
            option_element.textContent = subListArray[i].split("|")[1];
            pay.appendChild(option_element);
    	}
    }


    else if (payment == 2) {
    	for(var i = 0; i < pay.options.length; i++) {
            var option_element = document.createElement('option');
            option_element.value = "";
            option_element.textContent = subListArray[i].split("|")[1];
            pay.appendChild(option_element);
    }
}