Looking to poison the protagonist of a story, who is inside a home currently (not their own). Poisoner is a third party outside the home, and I was considering having them come to the front door as a salesperson or delivery man. I'd also appreciate suggestions not specific to these circumstances, just for future reference.
I'd like to suggest the way romans emperors used to have: rings that contain a secret container that holds the poison (normaly in a dust-like form). It's very discrete and quick to apply.
To fit the situation you mentioned, I suggest that the person who will poison the protagonist should be handing samples of this new "juice" door to door. He would simply put the poison in one plastic cup filled with juice and hand it to the protagonist (to look less suspicious he could also have more plastic cups).
The only problem is that I don't know what poison it was (the name), but I'm sure a short research and you'll find the name (if you don't already have a poison).
Posing as a food delivery man, the assassin poisons the food. Fairly straightforward.
The assassin does some mischievous plumbing work and poisons the family. Perhaps installs a pipe that is coated in some poison?
The air conditioning is broken? Okay, the assassin fixes it and also rigs it to pump out nerve gas.
Swap some advil with some poisons and tehy won't know what hit them.