What is the ruling on earnings acquired from a source suspected of being illicit, such as an employer who sells defective goods or a person who may infringe intellectual property rights?

The questioner's salary is permissible as long as her work is lawful, does not involve direct engagement in forbidden acts, and does not assist in them. What she mentioned about the employer or those she gives lessons to does not affect her salary, because the one who commits the negligence or violation bears its burden. It is permissible to deal with someone whose money is mixed, especially if the lawful portion predominates. Sheikh al-Islam clarified that whoever is ignorant of the situation of the one he deals with, and does not know that there is unlawful money in his possession, then abandoning dealing with him out of piety is a blameworthy form of extremism. The unknown is like the non-existent, and the default assumption for what is in a Muslim's possession is that it is his property.

If a man is known to have unlawful money, then dealing with him should be avoided out of piety. As for a Muslim whose affairs are concealed (i.e., not known to be involved in unlawful dealings), there is no doubt in dealing with him in the first place.

One must beware of intrusive thoughts (waswas) and doubts, and turn away from them.