I recently purchased a Sigma 28-70mm 2.8 EX from fleabay, and have to say I'm quite disappointed. It seems that at 70mm, anything shot wider than f/8 is a sloppy mess. Now I expected some degree of softness per my research, but this, to me, is unacceptable. Also, the seller admits to having the lens serviced at a shop in GA, so I wonder if that's not contributing to the issue. the zoom ring is incredibly tight as well, so I'm wondering if it's just a case of poor workmanship on the repair?? Anyone else have issue with this lens, or is it a function of Sigma in general (my first Sigma lens)? I'm in talks with the seller about a return, but the initial conversations make me think he is reluctant. Thoughts?