This Lincoln Wheat Cent was damaged by someone applying heat solder to the coins obverse and reverse. It is not uncommon to see this type of damage.
This coin was soldered as the above coin, and it is scratched. However, the reverse was completely covered in the metal.
Solder was sometimes used to repair coins, but the below examples must have been made by a person with some time on their hands. Any coin that's repaired, no matter how well, it still a damaged coin.