Book called Numismatic Forgery is absolutely brilliant. Talks about how different coins can be forged depending on era, how making technique should match the original coin (ancient coin dies were hand engraved, so should the modern forgery). Some coin forgeries are made from remelted coins of same era but of lesser value, so that metal would match etc.
Another example is Konrad Kajau, of Hitler’s Diaries fame. I may be mangling the quote but I recall is as being something like “Fake? Real? There are efficient documents and inefficient document.”
Eric Hebborn is a brilliant example:
https://en.m.wikipedia.org/wiki/Eric_Hebborn