I am not a Zeta player. I have about 20 cities in Delta and I play quite actively in an alliance that is rank 3 there.
I have had my fair share of good and bad experiences in Grepo alliances. When I first started, I confess, I was a complete noob. No idea how to play, no experience in games like this. I was asked to become a spy in an enemy alliance. I accepted, thinking this was a regular tactic and an accepted practice here. I passed on info, but my "teammates" in the alliance I was planted in kind of grew in on me. They became friends, and my loyalties at that point were not very strong to anyone. I stopped spying and passed on false data for a while, until they suspected and started attacking. My new alliance protected me and eventually won a war against my old one, and the old one was disbanded. (This was when the biggest player had like 15 or 20 cities. I had 1.) I eventually outlived this alliance, and grew on. I had good and bad times, being a commander and authority figure in an MRA, joining a renowned training alliance and working my way up there, and then being kicked for a noob mistake, losing credibility among old friends, and becoming a refugee, hiding in various places and moving my cities.
In my current alliance, and the one before that, I had to deal with spies. One spy had been among the "loyalist" group and was thought to be one of the most active and loyal players to the alliance. He was proven a spy, which he tried to cover up with a web of lies and deceit. He had privately declared allegiance to the enemy, and there were witnesses to see it. And when he was attacked by our alliance and lost more than half of his cities, he had support from the enemy the whole time. His reputation sank quickly, from a loyal player, to a dirty spy. We had no compassion in our punishment. We took most of his cities and he was forced to regrow with less than half of his old amount.
I feel that spying is a dirty tactic, though it will always be a part of grepolis, as it is a part of wars in real life. Some people will find opportunities and chances in the field of spying, and others will seek to take revenge on alliances that wronged them in the past. There are many types of spies, but in the end, they will all be caught. They will all be punished and taught an important lesson. Any current spies in current alliances, hear me: you may think yourself safe at the moment, amidst the friends that do not know of your betrayal, but think about it. You are a spy. You turn against people who trust you, besmirching your honor and reputation. Spies in real life are punished by death when discovered, so what do you think will happen to you when the inevitable happens? A good spy will last a while, but nothing can last forever. Good luck, we're looking for you.
Have a great day, citizens of Zeta, and good luck with your own infestations.