A customer of Miko's who picks up crack for his friends, John also offers Miko's team the chance to work from John's house.
John has a large and well-kept house because he was a middle class businessman before he got addicted to drugs. John has gotten fired at work and had his wife and kids move on because of his addiction. Letting Miko use his house is John's way to hang onto the house and subsidize his crack habit.
It's in John's upscale home that Shaka first watches people smoke crack, and it's there that he starts to get desensitized to the terrible things addiction causes. By the end of his time there, Shaka has lost a lot of the respect and moral fiber he was raised to have.