This kind of shady business will be exposed sooner or later.
Tips
usage
勾当 is always negative — it refers exclusively to dishonest, illegal, or immoral activities. It is never used for legitimate business. Common collocations: 搞勾当, 肮脏的勾当, 见不得人的勾当.
mistakes
Do not confuse with 勾搭 (gōuda, to collude/flirt). Also note the pronunciation: 勾 is read gòu (4th tone) here, not gōu (1st tone) as in 勾画.