I would not buy it. That hole looks like a braze on for a rack mount has been removed. Without the support of the braze on you have a hole in the seat stay of what I believe is an aluminum frame. Aluminum can crack around a hole like that (steel can too please don't start a steel vs. Aluminum debate) and there is a fair amount of stress on the seat stay when riding. Get another frame (steel aluminum, carbon, bamboo etc.) that does not have unsupported holes in it.