new HasTurtle[MAX_PLAYERS]; // global variable, add this on top of yours cript

CMD:buyturtle(playerid, params[])
{
// allt he codes from /turtle here
    HasTurtle[playerid] = 1;
    return 1;
}

CMD:gotturtle(playerid, params[])
{
    switch( HasTurtle[playerid] )
    {
        case 0: // when the player has no turtle
        {
 
        }
        case 1: // when the player has a turtle
        {

        }
    }
    return 1;
}