I've been pondering this a little, especially since someone mentioned a knife used in someones death. I think it depends on the connection between the object, and the persons death... And also how much of that person might be left behind.
Would you purchase a "perfectly good" bed someone had died in? Peacefully? How about violently? (I promise, it's clean!)
How about a corvette, a'la Mythbusters, that someone had decomposed in? Or how about a car that had run someone over? I know someone who still drives the car that they accidentally backed over a toddler in ... I don't know if I could do that. No one was at fault, it was a (very!) tragic accident but..
Would you be more, or less, likely to purchase a firearm if someone had been manually killed with it? (Say, a bayonette, or pistol whipped to death?) vs shot?
Many of these are cause for reflection - or absolute refusal to own the item... but it does make you think. For some reason, I think a rope that someone used to hang themselves (or someone else used to hang them) would be bad luck.