Review on Merrell J034353 Breakwater Athletic Men's Shoes by Tony Pierce

I had previously bought the exact same pair in a size 9 and they fit me perfectly, slightly larger which was very comfortable. The new pair, size 9, was obviously reduced in size and very uncomfortable and tight. The problem is there are no half sizes so I would have to go to a size 10 which would probably be too big. I don't understand the reason for the constant adjustment of the product size. What's the meaning of this?