Easy. Start off with high demands and work your way down to your real demand. Let them think they've won.
If the TV cost 1100, and you only have 900. Ask for it for 700. They'll say no. And try to lowball you somewhere in the middle. It's as simple as that.
ASK HIGH, They'll reply low. Which is around what you really want. It works for everything too.
If you want a handjob. (which I dont know why you would). Don't ask for the handjob. Ask for the blowjob. To which she'll say no, and then she'll offer the handjob.