Replying to Do Serial Numbers Go On Receipts?

So I want to buy an Xbox 360 from this guy. The system is only like 6 months old so it's still under warranty. The problem is that he doesn't have the receipt for it so I wouldn't be able to claim the warranty if the xbox were to break. My plan is: buy the xbox 360 from him, and also buy one from best buy. Then I'll take the receipt for the new one, copy it, and return the system to the store (to claim the warranty from microsoft, you need either the receipt or a copy of it). My question is, would that receipt work for the old xbox 360, or do retail stores print the serial number of stuff like a video game system on the receipt?