I was led to believe, and I dont know how true it is, but just because they sell the big issue doesnt necessarily mean that they are homeless, sometimes they are provided with accomodation and selling the big issue is a way of getting them to earn their money as part of the rehabilitation into living in accomodation again, so he may well have a house.
The way I look at it is that if you life comes to standing on street corners selling a magazine, then they obviously need the money more than me, Im happy to buy a magazine, but I dont want to be harrassed into it either.