I think as others have said...common sense is the biggest factor. With how common Lionfish, Scorpionfish, etc. are...if they were that big of an issue, they wouldn't be so common. I've had close up, hands in the tank, experiances with Blue Rings...without knowing they were in the tank and wasn't too happy when I found out they were in the tank...regardless what others think, I'm not stupid.
Teeth...well, that's a different story. I used to hand feed my adult Hawaiian Dragon and she was a puppy dog. My friend, James, hand feeds his Stonefish and numerous species of larger Scorpionfish. Some called us crazy...some called us brave...we called ourselves experianced.
My basketball sized Lionfish used to roll over, belly up and let me rub his belly. Times like that, I couldn't refuse. I knew it wasn't gonna kill me...
But, who am I to talk, I keep big Constrictors and a giant, 7' Monitor in my house...some call me stupid. I call myself experianced, yet have fun with it.
Common sense...it'll get you very far, in life.