Sales Order - Discount on an Item when other items are present

Hi Guys

I’m implementing a Erpnext and I have a tricky case, the situation is this.

My client make a quotation for a repair service, if the quotation is accepted, the client pay the amount in the quotation but if the client do not accept the quotation, he receive a bill with the amount of quotation.
In other words, the quotation has a price but if the client accept the quotation, this price is discounted from the total.

Someone has any idea or advise?.

Best Regards