Installing OSX not working "Can't be verified"

Hello.

I am restoring some old MacBook Pro 2009 that didn't have a hard drive, so I can sell it or give it to a family member. I made a OSX El Capitan installer via flash drive, but everytime I attempt to install OSX, it says something like "This copy of the OS X installer can't be verified. It may have been corrupted or tampered with."

When this first came up, I thought maybe I had forgotten to eject the flash drive on my iMac, so I redid the "make it bootable" process in Terminal. I did it again, and it gave me the same error. I can't boot into recovery mode because it doesn't even have a operating system to begin with, and when I try to install one, well, that's the entire reason I am posting this.

Any help would be appreciated.

mdp1101