Free postage that isn't

I have just sold two items but been informed that the buyer had gotten the impression that the postage was free. I am certain I specified postage but only local pickup was listed.

The items show that pickup is free, not free post.  If your buyer wants the items posted and you are OK with posting, send them an updated invoice including postage charges

I don't think you can update invoices any more, gp. That was another 'improvement' that ebay made, I think. 

You can still update invoices before payment, but not after.