I differentiate between corruption and scam.  Corruption, for me, is claiming to work for the general good, while working for your personal advantage against the general good ; or, having received privileges for the general good, and using them for your personal advantage against the general good.  A public function gives power and public means to somebody who is supposed to use that power and those public means in the general interest.  If he uses it against the general interest, and for his personal advantage, then that is corruption for me.

I don't see how you can be corrupt in a free market where nobody received any privileges, any public means, and nobody is supposed to do anything else but to serve his own personal interest.

A scam is simply, and on purpose, not honouring a contract (because you put terms in it which you knew you couldn't or wouldn't honour). 

Selling you some pills that make you 20 years younger, is a scam, because you have no idea how to make such a pill, and no intention to give me one.  You give me something else, and so you don't honour your part of the contract.