Q: Can’t download additional components needed to install OS X

Is Maverick what you are running? When trying to set it up for resale you erase the hard drive,  thru the recovery partition,using disk utilitiy, and then use the reinstall.  https://support.apple.com/en-us/HT201065

When using Command R or Command Option R,what is your internet connection. Wifi or ethernet?  https://support.apple.com/en-us/HT201314 This seems to prefer WIFI over ethernet. And WPA2 . When in recovery thru Command R, you have a help option that opens safari in recovery. You can check the internet connection by doing that. If you have a problem not connecting or lagging,that could be the problem. Also, Did you erase the full drive or just the indented volume?

Did your machine come with Mavericks installed?

If not, you cannot sell it with mavericks. Any OS or app obtained at the app store is NOT transferable and its license is tied to your Apple ID and password, which will present major problems to any buyer. You will need to reinstall the original OS before the sale.

If it was the original OS, then you need to use Command + Option + R (internet recovery) to erase your drive and reinstall.

You need the original appleID you used when you download Mavericks the first time.

If you removed your computer from apple support before you tried to reinstall you can go to help in recovery and then Icloud and sign in with your apple id. Then sign out and go back to recovery reinstall.

Good. Make sure when you run the install that as soon as it starts and goes to the setup screen you shut it down. That will give the buyer a completely fresh computer.