You get a silver trainer card when you earn 3 stars. To earn stars, you can do the following:
1. Defeat the Elite Four.
2. Win any one Master Rank Super Contest
3. Obtain all Battle Frontier Colored Plates
4. Earn a Platinum flag in the Underground (capture 50 flags)
5. Capture all 493 Pokemon excluding even pokemon.
You don't need to get all 50 flags from different people btw. :]
Yeah I knew the steps, but...
So you're saying we can capture the flag of one person over and over again and it'll work?
Okay if that's so, thanks! ^^