I have a A620, so I believe it's similar. As the other's have mentioned, I try to lower the exposure so that it's not as bright. With a low exposure, it's easier to notice the deep, wet finish of the car. I generally use vivid mode, because it makes the cars look better
edit: And I also wanna say that usually I don't tone down the exposure that much. I find reducing it by 2/3-1 is probably the most you need to go. Later you can use photoshop to edit the levels or contrast (adjusting levels seems to give me better results).
I like this camera a lot, except for the fact that it doesn't have image stabilizer... It's not a picture of a car, but here's one of the best pics I've taken (yes, edited with photoshop afterwards) on a trip to Yosemite
