I'm by no means bragging, but I've only handled one venomous snake that I considered to really test the limits of my handling abilities (and this is out of various Naja, Dendroapis, even Oxyuranus), and by far the absolute worst one was a forest! Of course, all snakes are individuals and I'm sure there are many black and green mambas that are bigger terrors to deal with than this forest was, but for me, she was pure evil. She was the only snake that I've literally had to 'dance' with while hooking/tailing her to avoid her tagging me.
Forests should, under no circumstances, be considered a 'safer' snake to go with than anything. They have their own little tendencies that make them every bit as dangerous, IMO, as a mamba, king, or probably even taipan.
As for the dwarf kings on the classifieds, to me, they look different from normal O. hannahs. They have a more...petite?...head structure. However, I have zilch experience with kings so I won't comment further about their physiology. It may be best to wait until they've been kept in captivity for a while to verify their size. To give credit to what someone else already mentioned though, what's a king without the size?! Then again, I've never been a fan of dwarf retics either... Be safe.
-Chance
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Chance Duncan
1.1 Retics (1.0 Tiger Het, 0.1 Dark Lavender)
1.1 Olive Pythons
1.1 Woma Pythons
1.1 Ball Pythons (Het Albino)
http://www.rivervalleysnakes.com