The used processor will work fine...as long as it WORKS fine. You may be buying another defective processor. You may be buying one thats on its last leg.

The steps i would take are:

#1.
Connect to the processor and call lutron support and see if they can walk you through fixing the problem.

#2.
Assuming #1 didnt work ask if you can ship it in for repair.

#3.
Assuming #2 didnt work ask the client if they want to gamble with a used processor or replace the system.