Counterfeit goods are trying to slip into the market.
Tips
usage
蒙混过关 (ménghùn guòguān, "to bluff one's way through a checkpoint") is the most common collocation — passing an inspection, exam, or boss's scrutiny by faking competence or hiding flaws. Implies the deceiver is hoping to slip through unnoticed rather than mount a sophisticated con.
memory
蒙 (méng, to cover / blindfold) + 混 (hùn, to mix in / muddle) — "covering up by mixing in." Pictures the swindler mixing the bad goods in with the good and covering the seams.