Basic /pay issue

gistfile1.java

public boolean onCommand(CommandSender sender, Command cmd, String label, String... args) {
    //preconditions: sender is a Player object, Command is "pay", sender has permissions
    Player p = (Player) sender;
    if (args.length < 2) {
        //invalid syntax, not enough arguments
        return true;
    }
    Player target = Bukkit.getPlayer(args[0]);
    if (target == null) {
        //Output that player must be online (or use an OfflinePlayer object)
        return true; //Unless using OfflinePlayer
    }
    double money;
    //This is your problem area, instead of reacting to bad input, it is ignored
    try {
        money = Double.parseDouble(args[1]);
    } catch (NumberFormatException ex) {
        //Output that it must be a number
        return true;
    }
    if (money <= 0) {
        //Output that money must be a non-zero positive number
        return true;
    }
    this.pay(target, money);
    return true;
}

public void pay(Player p, double amount) {
    //Hook vault or whatever economy you use
}