Q:

How does one write a character smarter than oneself?

How does one write a "genius" character? I don't mean a scientific genius, or someone who is a prodigious talent in math or chess or something like that. I mean the following scenario (or an equivalent):

Character G (for "genius") is a criminal mastermind who has just devised a brilliant scheme to make lots of money
G is pursued by Inspector A (for "average"), an everyman detective who knows G is up to something and is itching to catch him in the act, even though he doesn't know what the plan is. In fact, A can't even imagine it because it takes special insight and/or knowledge to have thought of it.

It seems like brilliance of G's scheme (and of G himself) is necessarily limited by the ingenuity of the author. And if the author can't come up with a sufficiently ingenious plot for G to hatch, it's hard for the reader to believe that an ordinary person couldn't have thought of it ("Really? That's his plan? And Inspector A never saw it? How stupid is he?")

A:

You have several advantages over your characters:

You get all the time you need to conduct research.
You have time to think about each thing they will do or say.  You get to think through the implications of the situation they're in, and the effects of their actions.
You can constrain and adjust your story world so that your character can excel in it.
You can construct the story to guide the reader away from areas that you know less about, and toward areas where you know more.
Depending on the extent of your research and thought, most of your readers won't know as much as you do about the subject of your character's expertise.  Mostly you don't have to be smarter than experts, you only have to know more than your readers.  (Caveat: Some of your readers may be experts, and they may be annoyed at the flaws you and your characters exhibit.)
Your readers want you to succeed in entertaining them.  They will (sometimes, to some extent) give you the benefit of the doubt.
The Writing Excuses podcasters offer this advice for speculative fiction:  Take one unimportant detail and get it exactly right.  This can lull readers into accepting that you know what you're talking about, which gives cover to make up all kinds of implausible stuff.  This may also work for criminal enterprises.

A:

Primarily, cheat by writing the story backwards. Start from the end revelation of the implicit story (the crime) and progress towards beginning, iteratively removing any simplicity.
Start with the outcome, the rather simple final set of events that is to be discovered. Then take it apart: tools, witnesses, methods, motives.
Take a look at each of them. Whenever you see something overly simple, replace it with something ambiguous, deceiving, non-obvious, or outright fake. Unlike the real wise guy, you don't have to limit yourself to things they can do. You can modify circumstances, personalities, environments to fit your convoluted needs.
Then, when you have the whole set of utterly corrupted clues, start writing the explicit story, what the readers will see. Distribute the clues throughout it, and then have the investigator come to the right conclusions, correctly recognize lies and deceits, and present the outcome as result of detailed analysis, a set of random pieces matching in the end, ingenious mind combining them, while in fact it was constructed from a kit of parts with a builder's manual you have created before starting on the explicit story, and only made the process seem unguided while you, the writer, were the guide.
(just to add: this is how math exercises are written. How do you get that complex equation to resolve to "2"? Start with "2", then keep multiplying by expressions that resolve to identity, add expressions that resolve to zero, square both sides, shift expressions between sides, divide by some red herring, and when your equation looks mangled enough, write it down as the subject of the exercise.)

A:

One way would be to sort of "cheat", if that would be acceptable to you. What I mean is that you can try to find some good ideas in real life. Real life is full of strange and wondrous things. Google things like "top criminals of all time" or something in those lines to find a criminal that might suit your character or has made an interesting enough scheme to fit what you're looking for, then take the idea and change it enough that it couldn't be easily recognizable. You wouldn't be the first writer to search for inspiration in real life.
“Good writers borrow, Great writers steal.”  ;)

