Why am I allowed to choose a quantity of only 1 to 9 pieces for a given item?
Because we decided on this option for technical reasons and simplicity of site development. But that does not mean you can only order up to 9 pieces of a given item. You can order the same item several times. For example, if you want to purchase a service of 12 plates, you can order 6 plates twice. On your order summary, you will see two lines referring to the same item, with the quantities selected.