"I'll pay cash right now if you give me 10% off." Or I'll round down to the nearest thousand if that would be more than 10% off. Like if it was $2400 I would offer $2000, but if it was already $2000 I would ask for 10% off, not $200 off. 10% sounds like less than $200 and he can't imagine holding 10% where as he can picture giving away 200 bucks.