Sure, shippers have to use a little common sense.
But the USPS specifically tells you not to tape over the bar codes on printed labels.
The USPS is pushing "click it and ship it" (with a discount) either directly or through eBay. Millions of people are using ink jet printed shipping labels. Obviously, opaque tape is a bad idea. What about clear tape to protect the label? Why won't they say that's OK to use? Or isn't it? WTF?
Some tape will work fine. Like clear packing tape seems to not be a problem. But if you make 27 lines of scotch tape it seems to not work so well. No duct tape either!
If you have a good quality print, you can put tape over it and it seems to work ok, but if you’re almost out of ink, it may never scan with or without tape.
I get annoyed with parcels that have the bar code crossing the crease line where the box flaps close together. The bar code will flex, obliterating one of the bars, or more, and often the number right below it along the crease line. This seems to happen most often to packages going to houses along the busiest sections of the highest speed part of the highway. I get to sit dangerously along side the highway, punching in number after number to see what got obliterated, taking a two second operation into a two minute death defying ordeal. Or more.
Smaller print is better than bigger print for fitting the bar code on a flat part of the cardboard. The new labels for parcels that will be printed by the USPS are all small, like two inches long by one inch tall, something like that. This will help immensely. Every parcel will soon have these, regardless the method of shipping, parcel post, priority, etc.