If I were you I would tell him if he doesn't adjust to the agreed upon deal you are walking.
I think dealers can get some kickback if they get you to sign at a higher rate.
I bought my wife a new Mazda 3 in 2004. (worst POS we ever owned) The dealer and I had gone back and forth on pricing and were $500 apart on our trade when they gave in and decided to deal with me. Mazda had 2.9% advertised on their web site. When they presented the deal for me to sign they had 3.9% on it. When I asked how that affected the loan over the total pay back it came out to the $500 I said I wouldn't pay. The salesman said the higher rate was based on my credit rating. HA! My credit rating was 820. I told him if we didn't qualify for the advertised rate nobody would and I slid the unsigned paper work back at him. He got on the phone to the manager and immediately adjusted the rate. From now on if I think someone is trying to pull one on me I just go ahead and walk.