Why would you want to use this feature?
You sell car batteries and by selling a car battery the client will get a discount for his/her used battery that they are returning. (used battery needs to be loaded as a trade-in item. Click here for more info on trade in items, ( http://bit.ly/SiStockAdditionalInfo)
When selling the new battery, Smart iT will automatically load used battery.
You sell tyres and when selling tyres, you always need to load wheel alignment.
When selling the tyres, Smart iT will load the wheel alignment automatically.