They certainly had the potential to know, because Hitler made no secret of his periods of destitution and artistic failure. He wrote about them extensively in Mein Kampf, but it wasn't common knowledge amongst the population not because this information wasn't available, but because nobody really cared. For example, think about how many people today who support Hillary Clinton have actually read her autobiography. If politicians were judged exclusively by their private life, our global political climate would be very different.

And Joseph Goebbels was certainly good at manipulating information to paint Hitler as more socially respectable than he was. He'd been arguably a glorified postman during the war, but this was enough for Goebbels, who had a knack for the propaganda he'd been charged to create, to turn Hitler into a humble war hero.

Also, this was a period in which the German people were beginning to reject the aristocratic regime of Kaisers and Old Prussians (reflected in the class struggles of Europe at this time). What we view as unattractive in a leader today wasn't necessarily repulsive to Germans in the 1920s and 1930s: Hitler was very much presented as the modest Germanic everyman who wished to do nothing more with his life than relieve Germany from its post-war dissatisfaction. To a population that understood hardship, weakness, in this sense, became strength.