I use Australia Post real time postage calculator, and want to apply a $5 Discount for orders over $100. So in the shipping surcharge tab (see attached screenshot) I configured a negative amount (-5) for orders over $100. (As the minimum shipping amount is always more than $6, the shipping charge will never go to negative because of this.)
I tested and it seems to be working. But this way to apply shipping discount is not officially documented in the reference manual.
I want to know whether other people configure shipping discounts this way as well? Would this cause any potential problems as it's not officially documented/supported?
Use a cart promotion instead.
The thing is that in Australia people want to see the shipping fee being lower, even though giving a $5 discount against the order total is the some financial result. Perhaps I could name that promotion “shipping discount” that should do …