I am helping a friend get her Mac ready to sell. We recently attempted this on a 2009 iMac and ran into a problem. We used Disk Utility to erase the drive but after that there was no way to reinstall the OS. There was an option to reinstall it but when we click on that we were told that it couldn't be done because there was no internet connection. What should we do to avoid this problem with the current wipe?