In the Lead process if the BP wants to sale his own vehicle, user selects from Menu Action Buttons Actions>>Trade In>>Add Trade in Vehicle
User completes popup window with following mandatory fields:
- Make - The Make of BP's vehicle
- VIN - The VIN of BP's vehicle
- Mileage - The miles of BP's vehicle
- License Number - The License Number of BP's vehicle
- Calculated TradeIn price - The price of BP's vehicle
The user selects the 
button to add a TradeIn vehicle to lead.
The Trade In details can be found on the Trade In tab.
For more details, please refer to this page: Add Trade-in