I will agree with tricksterpup with the addition that when they get older, their feeding response is still high, but they will rarely, rarely bite. You can grab (without really being cautious) an older king snake off the road and not get bitten 99 out of a 100 times (at least in my experience). I caught one last year and, right after catching it, spent 2 hours finishing a movie before I went and set its tank up. LOL.
I think they're GREAT pet snakes. If not on par with corns, very close behind. They also come in a variety of morphs as well, but not nearly as many as corns.
When you hold a healthy king and they start trying to feel secure by squeezing your hand, you'll KNOW you have a KING on your arm. They are some strong snakes.
You DO have to get used to the little ones. They tend to musk and may accidentally bite you when hungry (crazy feeding response) - which, as tricksterpup has said - can be ALL the time. I feed my kings last... because if someone refuses a meal, the king WILL eat it.
IMO, you CANNOT go wrong in getting a king.