The rate of earning merit as a newbie is really difficult that I think even on average making 20 posts doesn't guarantee merit and such a user might not be a spammer rather trying to contribute, learn and others which include what you added on your post about those coming to make complaints.
Nope, the lower the rank, the easier to get merit.
I think many users give merit based on the users' rank and knowledge, if they're not that good, but they're still newbie, they can still get couple merits. But if they were Hero or Legendary, but they post like a newbie's knowledge, people won't merit them.
The higher your merit/post ratio, the higher your rank.
Users can delete their own posts, there were few users did that.