Again, ask the customer what they are desiring to make sure can be restored and do a restore for that customer.
If the files to be restored are actually in the backup image then NetBackup should be able to restore it.
If netbackup can restore 1 file from that backup image then it can restore ALL files that are in the backup image.
Do a restore and ask the customer to verify it. After they verify it they may ask for another restore.
Do the second restore for the customer and make sure the customer verifies it meets their needs.
Do another restore if requested but make sure the customer verifies it meets their needs.
Eventually the customer will wear themselves down and not have time to verify.
Thank them for helping you to verify that you are backing up everything they need for restoring their data and for assisting you in the restores.
I have one customer that does test restores of a different one of their servers each month. They have profile databases that they write to disk and then Netbackup copies that to tape. They do the monthly tests to ensure that everyone keeps sharp on the needs for the restores and then they also check all of the servers to make sure that the backups are running AFTER the database dump has been written to the disk and not before :)