You can simply state that the items are opened and powered up momentarily to make sure they are functioning before delivery. You can even place a note within the package stating such. Explain you personally do this so they do not have to be concerned about an items that is DOA.
One thing you should do is be very particular with the packing. Unpack and repack with care. Remember the old army field manual instructions - "Assembly is the reverse of disassembly." If you can take it apart, you can put it back like it was.
Show your love of your customer......