Intelligence/cleverness/expertise in the MU* World is one which is a fine line. To a limit, however, I think it is possible to play someone smarter than the player, but it should be done within limits. Realistically, there are some races on MU*s out there that would be unplayable if we were purely focused on playing 'at or below player's intelligence levels.'

Same thing could be said for several occupations. Should a player be allowed to be a fencer if they aren't one IRL? Should we limit occupations and skills to what a player knows?

This is where I think that players should at least put minimal research into occupations or skills. This doesn't mean write a thesis statement, but it means, 'If you want to play a pianist, know how many keys there are on the board.' or just having a little bit of understanding of your skills so you can RP them properly, and this can transfer to inteligence somewhat.

I have played characters from a bit below my intelligence to characters with intelligence that would make most humans feel inadequate speaking to it. The higher level intelligence often requires knowing a few things... but I'm sure there are smart people out there that spend years with 'brilliant' research ideas including ones that last for years on if water melts.

You can't learn cunning and raw intelligence. You can enlighten yourself on your character and a little bit of what they know.