Is it permissible to work in customs, knowing that its revenues are deposited into the state budget and distributed in the form of wages and services, and that the workers do not determine the customs tariffs but only enforce them, being regular police forces?

Working in customs is permissible if the customs duties are imposed in a legitimate manner. The default rule for imposing taxes and customs duties is prohibition, unless the state's public resources do not meet the needs of the nation and the interests of the people. In such a case, they may be imposed to fulfill this need, to the extent that serves the purpose without injustice. If customs duties are collected from goods owners in exchange for services rendered to them, there is no objection to that. However, if they are collected without any corresponding service, or in exchange for services whose value does not amount to the customs duty, then they fall under the category of forbidden "maks" (illegal levies) and taxes.