Program: 2073
Project: 2073
Buggy source:
@Override public boolean onCommand(CommandSender sender,Command command,String commandLabel,String[] args){
  if (!(sender instanceof Player)) {
    sender.sendMessage(MessageUtils.mustBeIngameMessage);
    return true;
  }
  Player player=(Player)sender;
  HumanNPC npc=null;
  boolean returnval=false;
  if (NPCManager.validateSelected((Player)sender))   npc=NPCManager.getNPC(NPCManager.NPCSelected.get(player.getName()));
 else {
    player.sendMessage(ChatColor.RED + MessageUtils.mustHaveNPCSelectedMessage);
    return true;
  }
  if (!NPCManager.validateOwnership(npc.getUID(),player)) {
    player.sendMessage(MessageUtils.notOwnerMessage);
    return true;
  }
  if (!npc.isTrader()) {
    player.sendMessage(ChatColor.RED + "String_Node_Str");
    return true;
  }
 else {
    if (args.length == 3 && args[0].equals("String_Node_Str")) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        try {
          if (!EconomyHandler.useIconomy())           player.sendMessage(ChatColor.GRAY + "String_Node_Str");
 else           changeBalance(player,npc,args);
        }
 catch (        NumberFormatException e) {
          player.sendMessage(ChatColor.RED + "String_Node_Str");
        }
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
 else     if (args.length == 3 && (args[0].contains("String_Node_Str") || args[0].contains("String_Node_Str"))) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        changeTraderBuySell(npc,player,args[1],args[2],args[0].contains("String_Node_Str"));
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
 else     if (args.length == 2 && (args[0].contains("String_Node_Str"))) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        changeUnlimited(npc,sender,args[1]);
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
 else     if (args.length == 3 && args[0].contains("String_Node_Str") && (args[1].contains("String_Node_Str") || args[1].contains("String_Node_Str"))) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        changeTraderBuySell(npc,player,args[1],args[2],args[0].contains("String_Node_Str"));
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
    TraderPropertyPool.saveTraderState(npc);
  }
  return returnval;
}

Fixed version (ground truth):
@Override public boolean onCommand(CommandSender sender,Command command,String commandLabel,String[] args){
  if (!(sender instanceof Player)) {
    sender.sendMessage(MessageUtils.mustBeIngameMessage);
    return true;
  }
  Player player=(Player)sender;
  HumanNPC npc=null;
  boolean returnval=false;
  if (NPCManager.validateSelected((Player)sender))   npc=NPCManager.getNPC(NPCManager.NPCSelected.get(player.getName()));
 else {
    player.sendMessage(ChatColor.RED + MessageUtils.mustHaveNPCSelectedMessage);
    return true;
  }
  if (!NPCManager.validateOwnership(npc.getUID(),player)) {
    player.sendMessage(MessageUtils.notOwnerMessage);
    return true;
  }
  if (!npc.isTrader()) {
    player.sendMessage(ChatColor.RED + "String_Node_Str");
    return true;
  }
 else {
    if (args.length == 3 && args[0].equals("String_Node_Str")) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        try {
          if (!EconomyHandler.useIconomy())           player.sendMessage(ChatColor.GRAY + "String_Node_Str");
 else           changeBalance(player,npc,args);
        }
 catch (        NumberFormatException e) {
          player.sendMessage(ChatColor.RED + "String_Node_Str");
        }
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
 else     if (args.length == 3 && (args[0].contains("String_Node_Str") || args[0].contains("String_Node_Str"))) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        changeTraderBuySell(player,npc,args[1],args[2],args[0].contains("String_Node_Str"));
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
 else     if (args.length == 2 && (args[0].contains("String_Node_Str"))) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        changeUnlimited(npc,sender,args[1]);
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
 else     if (args.length == 3 && args[0].contains("String_Node_Str") && (args[1].contains("String_Node_Str") || args[1].contains("String_Node_Str"))) {
      if (BasicExecutor.hasPermission("String_Node_Str",sender)) {
        displayList(player,npc,args,args[1].contains("String_Node_Str"));
      }
 else       player.sendMessage(MessageUtils.noPermissionsMessage);
      returnval=true;
    }
    TraderPropertyPool.saveTraderState(npc);
  }
  return returnval;
}