Shyster
/ˈʃaɪstər/
Definition 1 of 1
Pro Tip 1/3Negative Connotation
The term 'shyster' is strongly negative and insulting, used to express disapproval and distrust. 
After the scandal, the lawyer was labeled a shyster by the press.
Pro Tip 2/3Not Just Lawyers
'Shyster' often refers to lawyers but can be used for anyone who is deceitful in business or politics. 
That salesman was a real shyster, selling us faulty goods.
Pro Tip 3/3Colloquial Usage
It's a slang word and isn't appropriate for formal writing or professional contexts. 
I wouldn't use the word 'shyster' in a formal complaint.