I love this idea. A maximum discount or a minimum price should be something easy to set. People make mistakes and may type a discount by mistake (i.e: USD 100, instead of USD 10; or 100% instead of 10%). We should be able to set up a blocker on the maximum discount amount or percentage. This should be a great evolution for the quote tool.
Btw. you say "I know that there´s a way to set the percentage however, not a way to set a maximum value." - how do you set a maximum percentage discount? I do not see this option anywhere.