>> Rick, a hair dryer would work like an iron.
I've priced those, too. I would even have other uses for a hot-air gun. But instead I pick the old ones off, tear some of the cardboard under them, and/or plaster over old labels with new labels.
I also bring small corrugated boxes home from work, and use black Magic Marker to black out old markings. I'm very careful to hide any old bar-codes completely, and any fragment of an old address.
For bubble mailers, the shipping label I print from "PayPal" covers one side completely.
I recall seeing some postal regulation about not re-using old cartons where any printing is still visible, but if they can ship it once with "Newark Electronics" printed on the cardboard, I don't see how it hurts them any to ship it twice that way.