Sorry to hear your having a fright of a time getting your MBP Retina system setup.
First, I suspect you don't have any storage in the system. You'll need to open the bottom cover to double check as it is rare to find a MBPr system without any bootable OS (or recovery partition). The owner likely took the SSD out as it had his stuff on it and didn't know how to wipe it down. If you do need to get a new SSD think about getting one that has an external USB case with it so you can set it up off of a second Mac. Review this to check your system: Step 10 MBP Retina teardown
Second, You'll need to get a copy of Lion or Mountain Lion to install on this system Snow Leopard doesn't have the needed drivers and OS services for this system. In this case you'll need to bring your system into an Apple store so they can help you install the OS or have access to a second Mac system to download it from Apple's App store which is now the only way you can get the OS (Mountain Lion). Once you have a copy of on the second Mac, you can setup a USB thumb drive as a bootable drive and then use that to boot your MBPr system. With the OS files on your USB Thumb drive you can then install the OS files onto the internal SSD. If you are missing the SSD you can also use an external USB case to house the SSD and install the OS directly from the second Mac onto it and then place the SSD back into your MBPr system. Heres a good source for a new SSD for our system if it's missing it: Outer World Computing - MBPr SSD upgrade
Third, You'll need to check to see if your DVD writer is compatible with Mac OS-X. Some offer device drivers and will need to wait until you have the OS installed before you can set it up to work on your MBPr. Otherwise you may need to get an Apple external Optical drive.