How does the product surcharge work? Is it possible to apply a surcharge only to specific individual products?

You can apply a surcharge based on individual products or product categories - eg. +$5 for virtual products.

You can also combine a product based surcharge with another surcharge type. To do this, two separate surcharges must be set up - one based on product type (eg. +$5 for virtual products), and one based on another variable (eg. +$5 for overseas customers). It's not possible to configure this together a single surcharge (eg. +$10 for virtual products purchased by overseas customers).