@croydon - I agree, but with that said, I think it's a fairly safe assumption that extremely cheap clothing (especially if it's not on sale) was produced by sweatshop labor, especially if it was made in developing countries.
When you take into account the fact that it traveled so far to get into a shop and that someone had to have spent labor on designing it, creating the fabric and making the clothing, then you can see that money had to be cut somewhere to get such a cheap price.
We tend to take ultra-cheap clothes for granted these days, but they have to come from somewhere. And even if the clothes are made in America they often come from illegal sweatshop labor.
I guess what I'm saying is that if you really want to stop these practices you have to put your money where your mouth is.