[RajatPawar]

1) Use a bool variable. Consider an object like a pen.

pawn Код:

new bool:has_a_pen[ MAX_PLAYERS ] = false;
CMD:buyapen(playerid)
{
     if( has_a_pen[ playerid] == true ) SendClientMessage( .. "You already have a pen." );
     if( Money < ... )
     else
     {
         has_a_pen[ playerid] = true;
      }
    return 1;
}

2nd) PlayAudioStreamForPlayer