What is the ruling on working for a merchant who deals in bribery, and is the salary earned from this work permissible or impermissible?

Bribery is forbidden according to the hadith: "May Allah curse the one who gives bribes and the one who takes bribes." Your advice to the man was correct. It is permissible to work with him and take a salary if the matters are permissible. Dealing with mixed funds is permissible, as indicated by the Companions' dealings with the Jews and their taking wages from them.