My Canon 85mm 1.8 was not what I expected in terms of IQ and autofocusing accuracy. So I sent it back to Canon while it was still under warranty. There and back took about ten days. Now the lens is all I expected it to be. Wonderous.
In an ideal world, nothing ever goes wrong, but in this one they do. But the way Canon responded to this warranty work really was pleasing.
Life is good,