this is a scam that has been going around for years.
I work for a big delivery company (the yellow and red one) I used to work in customer services and take at least 10 calls a day from greedbay customers saying i have sold a phone/laptop to Nigeria and paypal say i need to send it with a tracking number to release the funds.
When i got these calls the customer had usually sold the item for way over the average RRP but if you just stop and think to your self why would paypal need the track number to release to funds? they can reverse to payment anyway with a dispute and you also have to produce shipping details in that case anyway. Also once it has the tracking number it is in the system on its way to where ever and sometime it is impossible to stop before it has reached it's destination also some delivery companies let the receiver redirect the shipment by the just having the track number so god knows where its gone after that.
We did have some training by our in house security team who are mainly all ex police man and they showed use a dvd of how this works in Nigeria there are team of people sat in internet cafe's or just in plane offices randomly sending out emails buying stuff off the web and taking a chance to see it the item get sent or not.There must be a lot of people getting scammed out of stuff or else they would not do it.