I had the same problem. After four years shooting with my 35 1.4 (much of which it was my only lens) I had zero problems. It was a love sublime. Then one day I notice the blur wide open. It's kind of nice to know I'm not alone.





Well, I sent it in to canon and they fixed it up for a tad over $100, and it's in perfect condition again. It's probably a known issue with a known fix. Maybe one of the elements likes to slip around.





Good luck, don't give up on getting a good copy by return or repair. Maybe you could ask the seller to pay for half the repair? Seems like a nice win-win.