And you've got to think about who the neighbours are, and the possibility that the house will still be worth $1 after it's fixed up.

There was a street of houses in Salford in the early 90's, I remember, where houses sold for a couple of hundred pounds.  They'd been a normal sort of price until a single antisocial family moved in, and terrorised the area. Everybody wanted out, nobody wanted in.

If $1 houses are available, and the homeless aren't buying them, there's likely to be a good reason.  I'd rather live in a relative's garage than take my children to live next door to a crack den, for instance.