Arrow buying

[Equinox]

I'm not very good at scripting so...
im trying to make a npc in a shop that takes gralats from you when you say Buy arrows. the script is like this:

if (player.chat=Buyarrows);
(playerdarts += 30);
(tokenize 10);
say2 here you go.;

It gives me the arrows but it does not deduct it from my gralats.
Help please?