When buying items on ebay listed as rookie card (RC) this only aaplies to that players 1st Major League set release card ie Donruss, Fleer,Upper Deck etc sets like Classic or Minor League cards do not Qualify as Rookies.
2 examples of this are
1. Derek Jeter's rookie year was 1993
This is not a rookie card
1993 Classic/Best #91 not a Major League set
This is a rookie card
1993 Bowman #551 is a Major League set
Be careful when buying cards that are advertised as rookie cards often these other non rookies are worth much less.
If you are not sure look the player up on Google or Becketts site