Vac 'N' Sew Will Give Customers $100 for a Used

Short Answer

Vac 'N' Sew will give customers $100 for a used vacuum cleaner, regardless of condition, when they purchase a new vacuum or sewing machine.This essentially reduces the price by $100.What is this type of discount called?
functional discount
captive-product discount
seasonal discount
trade-in allowance
by-product allowance