Don’t know how other states are. In Texas we have a 6.25% sales tax. But the trade in is deducted from the sales price before tax is calculated. So on a $25,000 trade in you save $1,562 in sales tax (6.25% of $25,000). So here, it would be better to pay $50,000 for the new truck with $25,000 for your trade-in than pay $45,000 for the new truck with $20,000 for your trade-in even though the difference in sale price is $25,000 both ways. Dealer gets the same amount so he doesn’t care.
I always ask the invoice price of the new truck. And they will typically show it after I tell them I pretty much already know in advance since it is available on nada.com, kbb.com, edmunds.com, etc. Then I ask what rebates and incentives are available. Again available on the web sites. And many dealers have a “value my trade” clicky on their web site. I do that and get their proposed value and print it out before going in. But I don’t tell the salesman. That value is likely much more than they will offer when you get down to talking trade.
So. Once they offer a price for theirs based on invoice minus rebates and incentives, if any. that I can agree to, I ask about the trade-in. When they give me a low ball number for my trade-in I hand them the printout from their own web site showing their stated value. That will bring a frown and some stuttering about how that was an estimate sight unseen. But since I adequately describe my vehicle for the estimate they have a very hard time explaining the difference.
That is when I start waltzing toward the door. It is all an annoying but necessary game.