This week in the repair shop we had a saxophone that came in with a severely bent neck. While we can usually straighten a bent neck this one is bent so badly it will need to be replaced. This can be a fairly expensive repair if not covered by our service plan. Some necks can cost $300-400 or more.
We believe that necks get bent the majority of the time due to the player not having a proper grip on the neck while assembling or taking apart. Do not simply hold the neck by the end where the cork is and try to do this. Doing it this way puts too much leverage on the neck and causes it to bend at the weakest point in the curve.
Make sure you have a hold of the neck on top and cup your hand gently over the octave key. This gives you much more control and now you can insert or take out the neck without putting undo stress on the curve of the neck. As always, you still have to make sure to avoid catching and bending the octave key post that sticks up from the main body.
Keeping the socket and tenon where the two parts fit together, clean and dent free, is also important. That way the neck will slide in and out properly.