Can a Muslim be a sincere friend to a kaafir?

I started a small business and I gave a Muslim brother some of my products to sell. This was about a year ago. The brother claims to have sold all of my products but he hasn't given me any money. I have been asking him for months now to give me my money.  He always claims to be "too busy" to come by and give me my money. However, he has all the time in the world to visit and mingle with kaafirs outside of his being "busy".  What should I do to get my money back?  I was thinking about taking him to small claims court. Is it Halal to sue your Muslim brother?  Also, can I make dua against this brother?  If so, can you give me the duas and some advise?

Praise be to Allaah. 

You could take him to court. If there is a sharee’ah court there, then praise be to Allaah. Otherwise you can take to him to a court of the country in which you live, but only after exhausting all possible means of getting back what you are owed, such as getting other people to mediate in the matter.   

With regard to praying against him, if it is quite clear to you that he intends to take your property wrongfully, then you have the right to pray against him.