Tech-savvy gamers have long been wise to the fact Steam has regional pricing on its store, meaning that some countries can get games much cheaper than you'll find in others, such as in North America. They take advantage of this by using a VPN, or Virtual Private Network, which tunnels your connection through another region and makes it appear you're using the service from there.
This allows those users to get games cheaper but also causes revenue loss for the game developers and publishers. After all, the prices for games are set based on economic realities in each region.
Valve is now cracking down on this by requiring customers to have a valid payment method from that country. This means that you'll be able to see the prices of another country using a VPN, but unless you have a valid payment method registered in that country, you won't actually be able to buy.
According to the updated Steam support page;
If you have moved to a new country, or are living abroad for an extended period of time, you can update your Steam country setting when you complete your first purchase using a payment method from that country. If your location differs from your current Steam account store setting you'll have an option to change your store region while you view your cart or as you complete your purchase
So while not impossible, it certainly makes life harder for those looking for a quick deal by using a VPN.
Some legitimate VPN users are also caught in the crossfire, however, with some gamers stating they use a VPN as Steam has no regional pricing in their country, and that games are far too expensive for them to be able to afford.