My comment wasn't meant to run counter to yours, nor do I wish to start a discussion. What I'm pointing out about being cautious when buying and using second hand market whenever possible really pertains to any manufacturer. My experience has been that every lens I owned from every brand - Minolta, KonicaMinolta, Sigma, Tokina, Canon - has performed to spec (some better in absolute terms, some naturally worse) with the single exception of Canon EF-S 17-55/2.8 IS USM, which is really a sad story better told elsewhere. However, I'm not claiming that my experience is statistically relevant.
It's a shame that Tokina and Sigma seem to be more affected than the other brands but I also remember Photozone had problems with 24-70 L, 70-200 VR, Nikkor 28/1.4 and some other lenses that should have been fine given the huge price. Also heard stories of a dud TS-E 17L on FM forums and I can only conclude that QC has gone way downhill with most manufacturers recently. Thankfully none of the lenses I bought for the last few years have been very new, and none were bought in a shop.
It's a shame that Tokina and Sigma seem to be more affected than the other brands but I also remember Photozone had problems with 24-70 L, 70-200 VR, Nikkor 28/1.4 and some other lenses that should have been fine given the huge price. Also heard stories of a dud TS-E 17L on FM forums and I can only conclude that QC has gone way downhill with most manufacturers recently. Thankfully none of the lenses I bought for the last few years have been very new, and none were bought in a shop.