Knowing that whoever builds a shipment is susceptible to human error (especially if it's me), I always use the Amazon packing list to double check for errors. I was doing it by printing it out and putting a check mark as I went. That was kind of a pain looking for each item, especially if there were 50+ skus in a shipment. So I started doing it with an ipad and using the binoculars to find each thing on the list. That worked better but still cumbersome and still somewhat subject to human error.
What I would like to have is an electronic sheet where you scan the UPC and the fnsku and if they match it turns that line green. If there is qty more than one it turns lite green until enough items are checked to make it turn real green. When the whole sheet is green you know it's good.
I can think of some objections to this:
If you are using scanpower workflow, the shipment should need not to be checked. What about various distractions (double checking prep, item vs detail page, quantty, etc etc) that could result in an item ending up in the wrong box? And more importantly, what if you have a designated employee building shipment and you would feel more comfortable doing this check? Or you just want to double check yourself?
The other objection is the fnsku label should cover the UPC, so this method won't work. I used to be anal about covering the UPC until I toured CHA1 last year and saw thousands of UPCs left exposed. Now I leave mine visible - I just put the fnsku label either perpendicular to or away from the UPC so the Amazon scanner picks up the fnsku, not the UPC. It has not been an issue. (If you still want to cover the UPC go ahead and do so and check last four of UPC manually)