miscellaneous questions

I have some questions regarding GC application. Thanks a lot for those providing oppinions.

-Name check. How does INS choose people for name check? Is this for everyone? Do they select according to name or type of job characteristics?
-Birth Certificate. Do I need to the original birth certificate? Can I the copy one. I only get one original certificate now.
-How is the turn-down rate for the interview of applying GC through marriage? I heard some real couple have troubles in passing interviews.

Happy new year!