Reinhold Hanish (Reinhold Hanisch) in 1909-1910 lived with Hitler in the hostel in Vienna. He wrote his memoirs which were published in US in 1939 after his death. According to the historian Brigitte Hamann, Hanish's memoirs are quite credible, with one exception though: you can't believe what he wrote about the drawings: "In the early 1930s he lived primarily selling "Hitler's originals", which he painted himself."
Hanish lived in Vienna, and not once Hitler tried to stop distribution of those images. Hanish was even put in prison for the manufacturing and distribution of counterfeits; the Nazis were quite annoyed by the well paid interviews Hanish had been giving on the Viennese years of Führer.
The circumstances of Hanish death had never been clarified: he died in 1937-38 in the concentration camp or in prison. Also he could commit suicide.
However, the demand for the paintings signed "A. Hitler" was very high.
On March 12, 1944 Hitler told his photographer Heinrich Hoffmann that more than 150-200 Reichsmark those drawings couldn't cost. At that time, the price of real and fake paintings of Hitler reached 10 thousand Reichsmark.
More of Hitler's watercolors: