Well just show that you are willing to walk away from the sale. Tell them the other dealers prices and tell them who. Dont let them keep you on a leash. If they dont accept say "thank you for your time" and walk away.
I was lookin at a GTO and test drove it ...loved it...but when it came time to sit down with my brother in law (he came with me since I wasnt old enough to take the car myself at the time) and talk to the dealer it got tough. I offered a price and the dealer said no. So I said thanks and left. He called me a few days later asking me if I was still interested. They will be on your nuts if you show you wont take their crap.
I ended up getting my 350z from a dude who was great. He even was amazed and told me it was great that I knew about the car more than he did (most guys wont admit this if they try to sell you a car). When I drove it to my shop to get it checked out I told him I would talk with my dad and it would most likely be bought...gave him a ballpark and he accepted. Me and my dad came in offered a LOWER price and he accepted. Thing is I let him know from the start we wont take any bs. Keep it in mind
