Rule for allowing purchases based on country I'm running a commerce shop where we're gonna sell stuff we don't have worldwide rights to. 

By using the countries module I've ticked of which countries we can sell each product in by having a countries field on products. (see screenshot below).

I'm thinking it must be possible to make a rule banning to sell a product in a territory that hasn't been ticket of. It should be the billing country of the customer that needs to be validated against what countries the product is sellable in. 

Any ideas on how to configure a rule (or another solution) that does this check?

Cheers
You can use Smart IP to determine the location of the user and with the help of drupal views, you can filter the products not available for sale on that country.

That means only the products which are OK for sale in that country will be displayed to the user..