On the other hand, I sometimes also do something similar (not the same, but similar). If I (rarely) receive a merit, I always check who was the user who have given me that merit and if he/she is not a Legendary, I usually chech the post history of him/her and if I find something that deserves a merit I usually give a merit too.
I'm doing this because I know how hard is to create such a quality content that will catch the attention of those members who still have some merits. I also still have some smerits because I have little time to read and write here daily, so my way of working in connection with the merit is that if I receive some, I'll check if I can also give it or not.
Please let me know if it's not a good practice but I think it's understandable and acceptable (I hope so).
The key point is whether the user deserves a merit. I would say that reading a user's posts to see if any of the posts deserve a merit is fine.
The problem comes if these are the only merits you hand out and there is a pattern.