I'm about to jump into the world of DSLR. I've seen several people talk about getting a bad copy of certain lenses and then returning them to be tweeked or replaced. How does this process normally go? I'm interested with Canon, Nikon, Sigma and Tamron brands.
How do you prove that a lens is just not working for you. For example, it won't focus on infinity, etc. Do you pay for fixing if it's out of warranty? Do you pay for them to them to ship it back? Are most sellers willing to give you a different lens if the one they send you doesn't work? I'll probably buy from B&H, Adorama, KEH, and beachcamera/buydig, and maybe sites like sigma4less and other brand specific sites.
I would hate to just sell a messed-up lens to the next sucker. (karma!)