Currently, if your taxes are under the rebate, your tax incentive is only as good as your taxes are. So if you owe $3k in taxes, you're only getting a $3K tax incentive, regardless of if it's new ($7.5k) or used ($4k).
I'm seeing the government giving us easier access to that $3K… not granting the full 4k or 7.5k. For simplicity's sake, the full rebate is applied at the dealership, but the difference is still due for that year's taxes.
While governments can't directly manipulate Lemmy, you should still operate on the assumption that nothing you do here is anonymous.