Hm. Is it against the rules to revive a month old thread if the alternative is me posting pretty much the same thing?
Anyway, yeah, this is a pretty big issue. Some countries require VAT to be charged on orders and most websites include that in the price you see before you add it to the basket, but not Instant Gaming because....reasons? It also has started doing small fees for PayPal usage as well recently, which could do with being added in as well.
Example: Call of the Wild: The Angler is showing as being £10.55 on Instant Gaming. Adding it to my cart results in being asked to log in, upon which it sets my country to UK which introduces the needlessly hidden VAT fee. At this point it is actually £12.66. If I want to use PayPal, it becomes £12.89. Far from the other deals listed on the keyshop section.
To compare, Steam includes the VAT if required in the price shown on the storefront and in your cart. What you see is what you pay. It breaks it down in the receipt after payment; e.g "Subtotal: £8.32 Tax: £1.67 Total: £9.99". Which is how it should be, really. So yeah, would super appreciate taking these things into account when listing their prices on GGD because it's a huge annoyance.