My brother owns a store, but as soon as he hired a sales clerk, his sales underwent substantial losses and his customers decreased. Does this have any relation with religion?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

There is no connection between hiring a certain person to work in the shop and the increase or decrease in the profit. Rather, having such superstitious and pessimistic thoughts is prohibited.  It was narrated on the authority of Ibn Mas‘ood that the Prophet, sallallaahu ‘alayhi wa sallam, mentioned that belief in evil omens is Shirk. (Polytheism)  [Abu Daawood, At-Tirmithi, An-Nasaa’i and Ibn Maajah] Being pessimistic is a practice of the people of the pre-Islamic era of ignorance.

However, the existence of acts of disobedience in a particular place leads to the removal of blessings, and hence deprives its owners from such blessings. The Prophet, sallallaahu ‘alayhi wa sallam, said that a person might be deprived of provision because of a sin he committed. [Ahmed and Ibn Maajah]

This may also be a test from Allaah for your brother for a wisdom which only Allaah Knows. Therefore, your brother must be patient and follow ordinary means to develop his business and solve any problems facing it as he is only required to take the permissible means to gain his sustenance and Allaah disposes of the provisions as He wishes.  

Allaah Knows best.