I remember many years ago, a truck was stopped in Italy that turned out to have, depending on which story you believed, 5,000 or 50,000 large, blank sheets of paper. Blank....except for Dali's prominent signature on them. "Yes ma'am, this is an unauthentic Dali painting. We had the signature authenticated". I guess the next line is" and would you be interested in this week's special deal of free aluminum siding w/ each Dali painting"? If they stopped that one truck, how many didn't they stop?
Chagal was infamous for sending off a small, cursory sketch to the lithographer's, w/ instructions on how large and how many of them he wanted. The lithographer, an artist-in-reserve, the neighbor's dog, SOMEBODY did their best to create a large version of Marc's little sketch. When they were finished, they were sent to "The Master" to be signed and dated. If you bought one, you had better have been told that it was "after Chagal", but don't bet on it. If you buy ANY Dali print, you deserve what you get. In the Renaissance, it was common for an established artist to have his students paint the entire work, save for the faces and the hands. Hands especially are tough.
Then you had Georges Rouault, a very talented artist (especially if you like pictures of Christs and prostitutes, and who doesn't?) that was starving to death. The famous art dealer Ambroise Vollard tried to help him by commissioning a series of beautiful color etchings based on some of Rouault's paintings. I'm not sure how much he actually tried to help him, vs exploit him, as he had Rouault sign an exclusive contract for everything he produced. Period. He also gave him a small room to work in above his gallery. Maybe a bowl and some newspapers spread out in the corner, I don't know. But Rouault, being the perfectionist that he was, kept reworking and reworking the plates endlessly to get them just right, while Vollard cooled his heels and wasn't able to print the series until many, many years later. Art is neat. And it's all diddly until you walk into a museum and see a Beckman masterpiece next to another Beckman masterpiece, and it stops you dead in your tracks. How it got there, who really painted it, who authenticated it, mean very little then.