Is it allowed for the salesman to wear saree, niqab etc (female dress) for display in front of customers?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is not permissible for a man to wear the Niqaab and other clothes that are peculiar to women, even if this is just to show for customers.

Abu Hurayrah said: "The Prophet cursed the man who wears the dress of a woman and the woman who wears the clothes of a man." [Abu Daawood]

If a person says that he did not intend to imitate women, the answer is that he did what is specific to women and it is not a condition for the prohibition that he must intend to imitate them.

Ibn Taymiyyah said while elaborating on imitating the non-Muslims: "This is (prohibited) whether the Muslim intends to imitate them or does not intend it, and he only does so because he is accustomed to it. He is not permitted to do something that is peculiar to them (non-Muslims)." [End of quote]

Ibn 'Uthaymeen said: "If imitation is done, then the prohibition is committed and its ruling is confirmed whether it is with or without an intention." [End of quote]

It should be noted that a man working in selling women's clothing could lead to temptation because of the frequent contact with them and talking to them. Therefore, it is women who should be specialized in selling women’s clothing, because being on the safe side regarding one’s religion is of unrivalled value.

For more benefit, please refer to Fatwa 217450.

Allah knows best.