Can I accept money from someone (Muslim or non-Muslim) whom I know (or who stated) he earned it from a source mixed with Haram earnings that may have interest, or earnings from cheating on taxes or international trade fees on them?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

A group of scholars state that it is permissible to accept a present from someone whose earnings are mixed from Halal and Haram because the Prophet (Sallallahu Alaihi wa Sallam) used to accept presents from the Mushrikin (those who associate partners to Allah….), the Jews and others.

According to the above evidence, there is no harm, Insha Allah, in accepting the gift.  But you have to have the intention that you are making use of the Halal part of his money, as mentioned by some people of knowledge.

Allah knows best.