Using poison is as easy as well s**t on a stick. If you will pardon the example.

"That's a nasty infection you got there, what happened"
"I dunno, some loser poked me with a stick. Go figure"

I think a bigger issue is who is using the poison and the type of poison that is being used.
Any bum can let a dagger go rusty and give you tetnus but it takes a really proficient alchemist or
herbalist to be able to mix poisons so that they become colorless, odorless, and tasteless. It would
also take a great deal of skill (or luck) to be able to handle/deliver the poison to the target without
harming themselves in the process. So it is ultimately up to who the posioner is.
AS for the good/bad issue, poison is poison, I just hope I have the remedy...