What does the word 'operator' mean in here?

operator

The actual meaning of the word in this sense (as used by Mark Rudman) is difficult to find in Lexico and Cambridge.

However, YourDictionary has

An operator is defined as someone who is shrewd or manages difficulties easily. An example of an operator is a person who is an aggressive stock trader. An example of an operator is a man who can get a woman's phone number at a bar.

And, we do have business operator and political operator in common usage.

Facebook’s chief, once uninterested, has transformed himself into an active political operator in the Trump era

WSJ

LawInsider says...

a business operator as defined in the Freedom of Business Activity Act of 2 July 2004,

And I also find...

Leader, Manager, Operator--Which are you?

Forbes

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What does the word mean in (sic) here?

I believe that in this case it is a usage of a modern meaning that refers to shady deal makers and local politicians of of the 1850s. As far as I know, the word was not commonly used at that period of time to describe corruption. There were other words. To confuse things even more, Faulkner was writing about fictional events which had supposedly occurred a century before.

Any Faulkner reader will tell you that it no doubt refers to the nefarious actions of the Snopes family and their hangerson. They were an inherently corrupt lot, and often overly-appreciative of their own business acuity.