We don't have the worst of it. Check out Eric Hebborn's autobiography (short CNN piece about him:
https://www.cnn.com/style/article/ar...ger/index.html)
He was an art forger who was an immensely talented artist (and so could pass off his own work as old masters), but who also did things like used original paper and canvases from e.g., the 16th century, researched the pigments that the guy he was imitating used, and then mixed his own paints using the original formulas so that they'll be historically accurate upon chemical analysis.
Hebborn never claimed that his paintings were original (and he didn't sign them with forged signatures), he just painted them to look like old masters and let his customers think whatever they wanted. They ended up in major museums and big collections around the world. (He also died under mysterious circumstances in 1996.)
Baseball card world has a forgery problem, but the art world has it even worse.