It means that he buys bulk merchandise for resale.

However, most of these stores only deal in bulk merchandise; they aren't set up to sell to individual tourists and the window-shopping is not very interesting.

Usually there were several men sitting on the board porch among barrels of bulk merchandise, chewing tobacco and whittling; but today they were all inside.

Forum Robinsons is a complete one stop shop with everything "in between"-from the smallest items to bigger or bulk merchandise.