I'm a little rusty with the mechanics since I havn't played much recently. But I think can help a little. First off, I believe the game rolls your espeionage success individually for each character. And if a character is detected they roll on their combat rating to decide what happens to them, roll to low and they get injured or die. Now when it comes to detection, each regiment and ship guarding a planet has a detection rating, which gives them a chance to find a character. So far so good, with no general in place, you would easily be able to spy on them and destroy their stuff. The problem is the commander. Since you are talking about using infiltrators and lando (a bad idea, lando is a useful diplomat and comander aswell as a research character) im going to assume you are playing rebellion. And I'm going to guess that you have not captured Coruscant. When a planet has a general on it, each of your units has to roll against the general Leadership rating to succeed. And Most imperial officers have high leadership and they get a 50% boost while the emperor is on Coruscant. So you are rolling 50 espionage (infiltrators) and 80 espionage (Lando) against 150+ Leadership. Thats why your missions are failing. You might want to try capturing the general, as then you will be rolling your combat rating against his combat rating. Or leaving the planet alone for the time being.