Every order which isn't on status shipped can be canceled by the seller for any reason.
If the order isn't paid for when it gets canceled there's no problem.
Orders which are already paid for and than are canceled will be charged by Paypal with their transaction fee.
This is a policy that was introduced by Paypal recently.
The fee will be charged on the sellers account, despite the reason for canceling. The buyer will receive a full refund.
This isn't always fair in our opinion, cause sometimes buyers are causing the cancel. However we can't do much about this, so a few things that a seller can do to minimize this risk:
1. make sure you're market offers are up to date. Many cancels are caused by bottles on the market that aren't available anymore
2. If you want to cancel an order for whatever reason please do this as quick as possible. If it isn't paid for there's no transaction yet so there won't be any fee
3. Remove all destination countries you don't ship to in your shipping editor. This will avoid unnecessary order from buyers that are based in these countries.