custome discout not in system already

[cashaber]

I can really use this and quickly. 

I need to be able to put in a custom discount not already in the system.

Example,

A customer comes to me and says this item has some damage on it I would like it at a lower price because I still wish t buy it.  I'd agree and ring up the item, however I do not have any discounts already setup for this and I cant take 10 minutes to goto my house open the square website and make the discount.

there should be a way to do a discount right away with out having to make on for 5 10 15 20 25 30 40 50% or even 5 10 15 20 25$ off I have a $1000 cacl right in front of me and I cant do these basic things?????