Merit was made to determine one's post quality.
If someone buys and sells merit it means that he abuses the system.
I can guess that Merit trading is forbidden and those who try to trade Merit will probably get their thread to be deleted.
Merit also very helpful as it gives users the option to thank other users for their posts.
An ability that wasn't available before.
I'm agree in you. Some post gives us more idea about the topic and what really happening in the bitcoin or altcoin. Because of the Good quality post, we understand deeply what really he/she wants to say to us.