Yes because it is not a thing to people it is a person to people in real life.
If it is a terrorist threatening people, then it is a person. If it is a bomb, then it is a thing. If you are lost, then it is a place.
No, popularity is an abstract noun. You may see that many people like the person or the thing, but those are people; you can see the person or thing that people like; but you can't see or hear the popularity, the popularity is something that you know or understand about the person or thing.
people who buy a certain thing or a person/thing that eats it
The noun team is a word for a thing, even if the team is made up of people; a team is an entity, not a person.
There is no such thing as a flawless person.
The only thing I've ever given a homeless person is my special variety of STDs
b. can improve a person person's personal life.
A player is a person participating in a sport or in a game.
The most common thing for a person to say in the morning (to the first person or animal seen) is,"Good morning!" Some people shorten it to just, "Mornin." Other people follow that comment with asking if you slept well.
thing
Probably the person who did the good thing was not doing it to get a reward, so no.