Tools normally "traded-in" are given an "established and agreed upon value" by both you and/or the driver, and then that $$$ amount is applied to either your purchase or to your account if you have one with the driver.
Keep in mind that in many cases, the value of a used tool traded in if often or at last is usually less than if sold outright to co-workers or professional techs in person often making it somewhat a push-pull situation. Drivers are well aware of tool values including other truck brands and big-box tools.
If you have a long standing account with a or any driver they may offer you more, but as mr. Shaun and Chad have pointed out and I have seen first hand for years, the used tools they buy often resell quick due to price but they also do make some level of profit when taking in the trade.
It's not a "free money in my pocket " transaction.
