Student or Learner
Original sentence: "You have a BMW, dont`t you?"
That's correct, "don't you?" would be common in AmE.
In American English, "don't you?" is, I believe, more common.
"On TOEFL, which tests standard American English, you must use a form of do if have is the main verb in the sentence."
"She has an exam tomorrow, doesnít she?"
This is a note has been extracted from a pamphlet has been collected from other books by a non-native speaker but, he didnít mention their authors nor documented sources. So, I am in no position to defend what has been said in that pamphlet.
What made me post this is that, two intelligent contributors said that it is common in AmE to use form of do in that question tag while in the above context it says it is standard one. Sum it up, I have reached a conclusion that the word standard means common, am I correct, please?
(Not a Teacher)
Think of it this way:
Standard -- "The way something should be done"
Common -- "The way something is usually done"
Just because something is common doesn't mean that it is accepted as standard.