I think there are a few misconceptions on your post.
Only the people who really want to improve and earn money will stay on the forum.
I agree with that part that people who want to improve will stay on this forum, but I don't agree with the "make money part". I'm sure this was one of the reasons why the spam started in the first place. People start making post to reach a certain number criteria, and didn't really cared about having discussions with other users.
Logically, it's better to give your Merit to someone who can give you at least the same amount in return.
You are seeing merit as a form of exchange, and you should actually see it as a form of connecting with others. You give merit if you like what you've read. You should not be expecting to get merit back, because you gave merit to someone else. Don't look to merit as a coin.
Well, my question is what newcomers should write to be guaranteed to receive Merit.
Well just try to have a real discussion with users from this forum. Read their posts, and try to see what they are talking about, and participate in their conversation. Use this forum as a forum, and not as a way to get paid.
Basically stop thinking about getting merit, and you will probably start getting some without even knowing it.
Thank you for this balanced and considerate comment. This is the first post I found on the subject of merit that deserves merit points. A shame I don't have any to send to you! Well done.