There is no sadder sight than a customer walking up with an expensive knife that has a broken handle. There is nothing I can do for them short of recommending that they send it back to the manufacturer and beg for mercy. It is cost prohibitive for anyone to replace the handle of a knife short of using duct tape.
Sometimes I see a handle that was accidentally melted on the stove. Other times I see a wooden handle that has dried out to the point of cracking or warping.
The most common culprit in the crime is the dishwasher. While it might be easy to toss the knives in with a load of dirty dishes there isn't a more dastardly act to perpetrate on a knife. While the temperature in a wash cycle does not come close to endangering the temper of the steel in the knife, the heat will cause some expansion of the rivets or screws that hold the handle to the knife. It's the repetition of the expansion and contraction over time that works things loose or causes cracks in both wooden and synthetic handles.
While I'm on the subject of dishwashers there are a couple other reasons to keep knives out of them. Damage to the knife occurs when the edge bangs into other objects. Also, damage to the wire basket of the dishwasher occurs when the sharp edge of a knife cuts through the nylon covering the wire frame and the exposed metal gets rusty.