So let me see if I got this straight.
...
Last I knew, sales tax is figured on the price paid to get it out the door.
Exactly, unlike Value Added Tax (as used in Europe) which is payable on the difference between what the retailer pays and what he sells for.
I suspect their argument goes like this.
The price is quoted as $1500, with a rebate (not a discount).
The sale is for $1500.
Therefore the sales tax is on $1500.
The instant rebate is a separate issue not covered by tax law, it is not relevant to the calculation. It follows the sale, even if instantly.
It may matter how the customer receives the instant rebate. It might be a separate payment for example, perhaps from the manufacturer.
A rebate doesn't sound to me the same as a discount, legally.
Don't expect common sense to apply here.