This store has two options:
Items that weigh under 2 kg can be mailed.
Larger items must be picked up at the store.
So the customer wants to purchase a large item: on CHECKOUT, can the flat rate mailing option be disabled (ie, not appear as an option on checkout)?
Becuase right now, no matter what the customer has added to the cart, they have two options to choose from... the flat rate simply can't be an option for the large items...