Is it permissible for someone who sells goods from outside a Muslim country to inside it to direct buyers to drivers whom he knows pay bribes, knowing that they have a choice between bribery and customs duties (Maks/ushur), and that customs duties are lighter than bribery, and that not directing them may prevent buyers from purchasing due to the absence of a reliable delivery method?

There is no harm for a merchant in guiding buyers to someone who can deliver their goods to them. Even if the drivers engage in illicit dealings, the sin of what they do falls upon them, and they should be advised to fear Allah. What they pay to avert injustice and circumvent the forbidden customs duty (maks) is not a bribe. If taxes are without consideration, or in exchange for services that do not amount to a customs fee, then they are among the forbidden customs duties (maks). It is permissible to pay the lesser amount to avert a greater harm, acting upon the principle of committing the lesser of two harms. A merchant's adoption of a scholar's fatwa (definition) does not preclude dealing with those who do not hold that view.