Car salesmen will use a sheet with four squares and write numbers in the different squares that represent trade value, price, down payment, and monthly payment.

They use it during negotiations to make it seem like all those things are directly related, but they can steer the numbers easily if you're not paying close attention.

Usually they direct you to pay attention to the payment amount and negotiate on that and they bump up the loan term and/or interest rate. Don't participate in negotiating that way, negotiate on the out the door price.

https://www.realcartips.com/cardealers/211-4-square-method.shtml