How can we improve WHMCS?

Currently, customers can order multiple quantities for add-on services, etc., but there is no limit on the number.

This is dangerous because if a customer places an order that exceeds the number offered by us, we may end up paying an inappropriately large amount of money.
It may also allow a large number of unwanted, malicious orders.

So we need the ability to set a limit on the ability to order multiple quantities.