How do dealers work out a price for my trade-in?

Dealers use the value listed for your make of car, together with the year model, as a base, and adjust up or down based on condition and mileage of the car

As a rule, a generally accepted mileage for a car to travel in one year, is 25,000 to 30,000 kms.

Mileage above that, in most cases mean an adjustment down from the book value.