Recently I ran across and issue where we could not install a fresh copy of OS 10.9 on a mac. The error on screen was “This copy of the Install OS X Mavericks application can’t be verified..”
The fix is relatively easy in this case. In the main menu when you first boot onto the USB drive (the one that has the option for disk utility, install etc), from the top of the screen menu, select utilities and then terminal.
Set the current date as such (in this example lets say the date is 3/14/2014 at 9:00am
Now exit the terminal by typing “exit” and then try to re-install as normal and you should be good to go.