Yes, it seems that they have a Senior+ rank that serves them to get easy karma points. User @Rancho returned to 2+ again, which supports my suspicion. -1 for him today, let's see in which direction this case will develop.
You're welcome, a little attention costs nothing, and if it can help us get those shillers under control, I'm always here to help.
That's exactly what I thought, but I must also tell you that I will be able to find out who it is. I won't do anything, I just want to observe that user's behavior to draw my own conclusions.
How are you able to find these shillers? Just curious! 
I had another question, might be a little off topic. By +3, did you mean you gave him 3 positive karmas? I thought one could give only 1 karma to a user within a certain period of time. To test this, I sent you 1 karma, but the second time I tried to send it, it didn't let me. Instead, it showed me this message: "An Error Has Occurred! Sorry, you can't repeat a karma action without waiting 10 hours." Can you please explain? Or is it a privilege that only a specific group of people has?
Shillers usually follow a very defined pattern when it comes to acting, if you read this thread in depth you will see that it is not very difficult.
Regarding your second question, the administrator and the president can send all the positive (and negative) Karma they want, there is no limit. Global moderators, by default, do not have that privilege.
Absolutely, for now it seems that only the admin, president and Global Moderators can give bulk of karma. Even 50 karma in one click.
Only the administrator and the president, and I think it is not limited to 50, I have never tried that amount, there is no limit.