Purchasing a used system is a tremendous gamble and we do not recommend it. P3 warranties are non-transferable and thus you have no warranty. You also may purchase a unit that is not working properly.
You should also be sure the serial number is 10000 or above. Units with a serial number under 10000 went End of Life on 6/30/2014. They are not eligible for support or repairs. Your only options are to perform a Serial-to-USB Upgrade (Contact Sales) or purchase a new package.