Nightwing mentioned it in passing (he beat me to it), but you can catch some images and thoughts on
The Master Mesmerizer of Metropolis on Nightwing's Superman web pages. Worth a look.
You have to remember (way back in early Action Comics) that Lois wouldn't lower herself to even spit in Clark Kent's direction (in fact, she probably barely gave the poor fellow a daily scornful glance); and that her view of Superman was the opposite: she was bedazzled, awestruck, infatuated (as was the general public, I suppose)... For all intents and purposes, Kent and Superman were two different people. Early on, neither Lois, nor any members of the general public, had a properly intimate relationship with either Kent or Superman.
Add to that MatterEaterLad's superb observation:
and its easy to not find a right answer when you aren't forming a question...
With early Superman, I don't find it a stretch to believe he could fool people.
Difference between Superman and most other DC heroes is that his civil identity Clark Kent is the fictional identity. If Superman's secret identity was revealed , Superman would go, but Clark Kent would be history.
Nonsense, Coldsam. Clark Kent is not a fiction. He is as real as Superman. Our hero is just as much Kent as Superman. He is one man made up of these two equally vital identities. Take that away, and you fail to appreciate just what a remarkable and intriguing character our supposed bland boy scout really is.