When I sold Hifi if someone asked for discount for cash we would automatically give up to 5% off. This was because if they paid on credit card we paid 5% in charges to the merchant services co so it was better to have cash in hand to spend on new stock. I wouldn't go over that unless there was good reason (We wanted shut of that piece of kit or if it was a VERY good customer and we knew we'd get a lot of business from it)
However we did have one bit of 'fun'
there was a young lad who tbh was a right pain in the rectum. he would come in week after week when new kit was released with a copy of What Hifi or similar and spend AGES, listening to it, comparing it with the review and generally wasting a lot of time(never buying anything). Anyhow it so happened that there was an amp released that was amazing for the money, they were like rocking horse droppings to get hold of. he came in and did the usual listen for 2 hours etc. then he asked how much to buy it, I was gobsmacked and nearly fell over! I quoted the retail price as I could sell them for that all day long. he started the "Practical Hifi will do it for £X less". Now I knew the guys there and knew they wouldn't discount this kit as there was no need to so I said, I'll do it for £Y which was £5 less than he quoted, he trundled off back to Practical to obviously try and beat them down further so I rang them up and had a natter with them, anyway, long story short, be effectively bounced him back and forward about 6 times till we got fed up, when he came to me I said, "Oh, I've just sold the last one!" so he ran back to Practical who did the same
He came back a week later and paid full price!