I have been searching here for how to get merits but the most common answer I found was by posting useful information. But I wondered how people give merits.
Yes, but not limited to that. Sometime a user can get merit based on his unique response to some questions or with humorous thought. A short but constructive answer can gain merits.
Its actually based on the sender's appreciation of the response. I am been noticing some can easily send bulk or good amount of merits by simple response. Cant actually determine the scale since there is no actual basis any user should follow in giving merits aside from the fact that you mentioned of being helpful and providing good source of information.