Do what I do when I buy a car.

Now you know the car, you know it's $20K, you know the dealer knows your interested. So when you go back, go back with a bank cheque for $18k. Listen to all his uneducated shit he'll throw at you, and go sounds good. THen when it comes to do the real deal, pull that cheque out and be absolutely ready to walk away,

He'll pretend as if you just killed his first born, then he'll say his boss will kill him, then he'll say some shit about not making any money from this (now is a nice time to inform him you honestly dont care about his problems). Then when you'd had enough of his excuses, just say you have 5 minutes to give me an answer or I'm out of here and I won't be back.

Guarantee you the car yard paid $15k for that car, and I guarantee you you'll get it for $18k. Don't accept any bullsihit like 'removing 12 months warranty' or anything.