looking at cars - make an offer?

[B Buddy]

I am going to look at a 2 or 3 cars this week.

2 are Mustang GT convertables, and one is a Nissan 350Z convertable.

They are all at car dealerships, and all have low miles on them and are 2006 models.

a. One of the Mustangs is from carmax, and it's selling under it's blue book value by about 4k, and it's their bottom line and final price.

b. There's another Mustang GT I like that has a few more features but they are asking about 5k more. I thought I'd offer them 30 for it. It's blue book is about 32k, which is what they are asking. I'll be carrying cash should paying cash help me get a better deal? I like this car the best, but it's close to the same model as the one at carmax with a few extras, and they are asking 5k more. I still haven't test driven any of these so i might decide to go with a nissan 350z but i'm leaning towards getting a mustang.

http://www.cars.com/go/search/detail.jsp...amp;aff=tenness

3. Nissan 350z - selling at about blue book. They are asking 30,900. I'd probably offer around 29-30k.

http://www.cars.com/go/search/detail.jsp...leadExists=true

Any negotiating tips, or suggestions on getting a good deal on a car w / less than 20k miles but not new (i'll be paying cash)?

Thanks