What is that word that is used to say someone "takes advantage of the situation". This word usually has a mildly negative connotation. It is related to being clever.
I am surprised no-one has come up with "a profiteer" (very close the word we would use in French: "un profiteur")
Definition in the Cambridge Online Dictionary:
a person who takes advantage of a situation in which other people are suffering to make a profit, often by selling goods that are difficult to get at a high price:
a war profiteer
Apart from the fact that not much cleverness is involved in it, it seems pretty close to what the person asking the question was looking for, seems to me.
For a word with less negative connotations, I would suggest the word astute.
Here's the definition from oxforddictionaries.com:
having or showing an ability to accurately assess situations or people and turn this to one’s advantage: an astute businessman