How do tariffs have a hope of being effective long term?

Let's say I want to buy X product from a country and there is now a 25% tariff on it. Rather than paying 25‰ more, why wouldn't I just pay 2‰ to some intermediate country (Mexico? Vietnam?) to have the product pass through their factories for some cosmetic process of a creatively dubious legal nature, and kill all the competition that tries to comply with tariffs? This artificial price setting stuff always results in blackmarkets