If possible (not everyone can do this) I would pay for your laptop with CASH so you don't have to worry about your cc being on the receipt and you can mail the original sales receipt to the buyer.
Well, to help answer my own question, the warranty from Compaq, clearly says the warrranty if valid only for the original purchaser. So, if you buy one on ebay or from someone else, and don't get the receipt, you won't have a warranty. I guess you can still get an extended warranty without a receipt, but it requires a phone call. However, two extra years of warranty from Compaq is a deal at $99.00
Compaq Extended Warranty