I always say, "You have (got) a car, haven't you?" and never "You have (got) a car, don't you?"

How many folks out there use the tag, "don't you" in THAT situation? I'm hearing it a lot lately. There IS a logic to it as the question could be HAVE you a car? HAVE you got a car? Or DO/DON'T you have a car?

Therefor the auxiliary DO/DON'T seems to have a claim to be in the tag!

I'd like to know other English native-speaker thoughts on this. Please.

Question

I always say, "You have (got) a car, haven't you?" and never "You have (got) a car, don't you?"

How many folks out there use the tag, "don't you" in THAT situation? I'm hearing it a lot lately. There IS a logic to it as the question could be HAVE you a car?  HAVE you got a car? Or DO/DON'T you have a car?

Therefor the auxiliary DO/DON'T seems to have a claim to be in the tag!

I'd like to know other English native-speaker thoughts on this. Please.

Answer

Hey Moira, I think you've touched on a UK/USA difference here. As a Canadian, I never, ever say "have" in question tags after "have" when it's indicating possession. I always use "do" like so:
You have a car, don't you? 
And formally,
You have a vehicle, do you not?

When "have" is functioning as an auxiliary, such as in the present perfect, I would use "have" in the question tag:

You've seen that movie, haven't you?