Instead of "instant rebate" think of what happens in the case of a more traditional rebate. For the traditional rebate, you pay the full price; pay tax on the full price; go home and follow all 13 steps required to get the rebate (cutting out barcode, copying receipt, printing name/address/info on proper form); mail documentation in #10 Envelope; wait 12-18 weeks for rebate to be sent to you only to find out that you missed one of the 13 steps required and are not eligible for the rebate.

Now with an "instant rebate" you pay the full price as you would otherwise have done and then magically all 13 steps are properly completed for you and at the very end of your transaction you receive your rebate by having said amount deducted from your total.

This differs from a sale in that you pay the sale price and not the regular price, followed by getting a rebate. Sure it's mainly semantics but that's most likely what's happening in the case of an "instant rebate".

And no, I am not an attorney