Discuss the issue with the customer and attempt to duplicate the problem. If you cannot duplicate the problem, discuss the process he should be following. If you can duplicate the problem, follow the troubleshooting guidance available on the Reseller web site to identify and correct the problem. You may also contact Intel customer support for assistance.
You are not required to perform troubleshooting, but if you can identify the problem or L4 for return, you will be saving yourself both money and time and will be improving your customers' experience. Since you are paying freight-in, it is to your benefit to determine what the problem is before returning the CBB (common building block) or L4.