In the world outside of numismatics, coating steel with zinc is known as galvanizing. It is a process used to protect the steel from rusting and which relies on the different electrode potentials of the zinc and steel (iron) metals to draw ions found in salts, acids and air away from the steel/iron molecules, and have them attach to the zinc molecules (the "sacrificial anode" in the galvanic equation). Eventually the zinc becomes saturated with various ionic atoms, and there is no longer a different electrode potential to protect the steel from rusting. The zinc coating needs to be replaced with a fresh zinc coating before this occurs (referred to as the first maintenance period) and this is done by removing the old zinc, and replacing it with newer pure zinc (reprocessing).
Periodically reprocessing galvanized steel parts is considered good maintenance practice in the industrial world, but is considered to be altering the surface of the coin in the numismatic world.
In the case of the penny in the
ebay listing, the reprocessing was done past the first maintenance period, and there are already signs of pitting and corrosion on the underlying steel.