[backcountryskier]

Regarding checking for decentering

Here's what I do. I buy a lens, take it home, put it on a tripod, target on the wall. Focus with live-view at max magnification. Focus separately for each corner. Sharpness should be about the same for each corner.



Compare to a lens with known characteristics (e.g. your 16-85 at 16 mm). Suppose for argument's sake the lens you bought has is supposed to be slightly weaker in the center but much sharper at the borders (according to photozone tests). Your non-quantitative test should reflect that.



Good luck trying to get multiple copies. My guess is that they'll charge your credit card for all merchandise you take home. Be sure to ask whether they charge a restocking fee.