I got the acceptance email, and they're giving a lil extra. A welcome surprise.
Congrats on the trade-in completion !!
The extra is just the sales tax difference. Google's trade-in partner is not that considerate to increase the trade-in value.
Depending on your state, the sales tax is calculated after the deduction of trade-in or for the full amount.
When you place the order, Google takes the sales tax for the full amount. When your trade-in is accepted, the sales tax will be calculated for the full price – the trade-in amount. And the extra sales tax amount you paid originally will be included with your trade-in refund.
For example, even though my trade-in refund for Pixel 9 Pro XL is $600, I'll be getting around $660 after the trade-in is completed, taking into account the ~10% sales tax amount in WA State. Your total refund amount will vary based on your local sales tax percentages.
Sorry if you are in the below states
-----------
From Google search
"The states where sales tax is generally calculated on the full, pre-trade-in price of a new phone are:
California
Hawaii
Virginia
Arkansas
In these states, you would pay sales tax on the total price of the new phone, and the trade-in value would be applied as a simple credit to your payment, but it wouldn't reduce your taxable amount.