This has probably be mentioned before but this place is relavent for it:
Dell Website Shop/Dell Outlet Shop coupon points for trade in Old Dell systems. The number of points should depend on the age of the system and also the condition.
An online chart should be made available telling you the approximate value of the system, this should be updated regularly. As Dells can be heavily customised, inputting the Service Tag might be used for a more detailed estimated. An additional checkbox/field can be put in for heavily scratched/broken systems.
For extremely old systems the coupon value for recycling can be quite small but would serve as an incentive for computers/electronics to be recycled properly and for users to purchase from Dell second time round.
If the above goes well you could maybe do this for non-Dell components including the following: TVs, Phones, Desktops, Laptops, Keyboards, Tablets, Printers and Scanners. Not too sure if that would be of much benefit but it might bring in some more customers. Naturally give a better discount of equivalent value to Dell systems than non-Dell systems as a loyality bonus.
Once Dell purchases the system; Dell can cannibalise it for the parts for sale on the Dell Outlet shop or sell it as a complete second hand system.