Long, long ago, Cliff and Judy Lawrence ran a few articles in their Pen Fancier's Magazine under the heading, "Pen Tricksters". Even back in the 1980s, people were "improving" pens without disclosing the work to potential buyers. As I recall, one of the "tricks" was cap lip replacement, hiding the seam under the cap band (a perfectly sound restoration method, if duly disclosed); another was reblackening -- though in one reported case it was the Lawrences who were in error, as they concluded that a Black Giant had been blackened since it faded when immersed in hot water (pristine hard rubber will indeed resist fading, but exposure to light will invisibly break down its surface; subsequent exposure to water will then result in instant fading).
I've seen my share of undisclosed repairs in pens purchased both online and face-to-face at shows. One that was completely new to me, though, is shown in the photo above -- the barrel of what looked like a nice clean unrestored Pelikan 100. Getting the filler unit out of one of these pens is delicate work, since the aged celluloid of the barrel is typically fragile. This is one of the few cases where soaking is an essential disassembly method -- which also has the side effect of loosening the barrel oversleeve (the "binde"). Which, once it slid off, revealing a whopping burn hole in the side of the barrel. The damage to the barrel must also have damaged the barrel's original binde. Someone then slid a new one in place over the hole, und Bob ist Dein Onkel.