You are incorrect. Read the fine print of an online order
“Trade In: iPhone 12 Pro and iPhone 12 Pro Max pricing based on trade in of iPhone Xs Max in good condition. Trade-in values require purchase of a new iPhone, subject to availability and limits. Trade-in values will vary based on the condition, year, and configuration of your eligible trade-in device. Not all devices are eligible for credit. You must be at least 18 years old to be eligible to trade in for credit or for an Apple Gift Card. Trade-in value may be applied toward qualifying new device purchase, or added to an Apple Gift Card. Actual value awarded is based on receipt of a qualifying device matching the description provided when estimate was made. Sales tax may be assessed on full value of a new device purchase. In-store trade-in requires presentation of a valid photo ID (local law may require saving this information). Offer may not be available in all stores, and may vary between in-store and online trade-in. Some stores may have additional requirements. Apple or its trade-in partners reserve the right to refuse or limit quantity of any trade-in transaction for any reason. More details are available from Apple’s trade-in partner for trade-in and recycling of eligible devices. Monthly pricing: Available to qualified customers and requires 0% APR, 24-month installment loan with Citizens One or Apple Card Monthly Installments and iPhone activation with AT&T, T-Mobile, or Verizon for purchases in an Apple Store. Taxes and shipping not included in monthly pricing. Additional Apple Card Monthly Installments terms are in the Customer Agreement. Additional iPhone Payments terms are here.”
The value of your trade in device is only an estimate until the final value is determined upon receiving the trade in. You get a cash credit for the trade in. The price of the new device is not a discounted price under consumer law. It is sold at full retail, and taxed at full retail. You get a cash credit for your device that you may, or may not, apply towards the price.
Sales tax would only be on the lower price if that was an advertised sale price. The price with a trade in is still the price as listed on the web site or in store. That is what you’re taxed on.
Even if you’re using the offered cellular specific trade in offers, e.g. AT&T:
- ”AT&T Special Trade-in Offer: Monthly Price reflects net monthly payment, after application of AT&T trade-in credit up to $700 applied over 30 months after trade-in of eligible smartphone with min. $95 trade-in value. Requires upgrade of an existing line (or activation of a new line in stores) and purchase of a new iPhone 12 mini, iPhone 12, iPhone 12 Pro, or iPhone 12 Pro Max on qualifying 30 month 0% APR installment plan, subject to carrier credit qualification. If buying on the AT&T Installment Plan with Next Up, customer is responsible and will not receive any credits for an additional $5/mo. for the Next Up upgrade feature. $0 down for well-qualified customers only, or down payment may be required and depends on a variety of factors. Tax on full retail price due at sale. Requires activation on eligible unlimited plan (visit att.com/plans/wireless for details). If you cancel wireless, credits will stop and you will owe device the remaining device balance. Activation/Upgrade Fee: $30. Must trade in eligible smartphone in good condition at a participating AT&T location within 30 days from activation of new phone. Trade-in device may not be on existing installment plan. See att.com/tradein for terms and to check if your device is eligible. Bill credits are applied as a monthly credit over the 30-month installment plan. Credits start w/in 3 bills. Will receive catch-up credits once credits start. Wireless line must be on an installment agreement, active & in good standing for 30 days to qualify. Installment agreement starts when device is shipped. To get all credits, device must remain on agreement for entire term and you must keep eligible service on device for entire installment term. Limits: One trade-in per qual. purchase and one credit per line. May not be combinable w/other offers, discounts, or credits. Purchase, financing, other limits & restrictions apply.“