I'm in England and it has started to charge me in dollars despite:

clearing cookies
changing page settings
changing account settings
refreshing account

No matter what I do it always changes it to dollars at the checkout.

Any ideas?

Check in the right bottom corner of the frontpage if the correct currency is shown.
Or do you mean this with checking page settings?

Isn't it cheaper for you to buy in USD even if there were any conversion fees? If that assumption is correct I'd see it as a boon. :P

I'm in Canada and I get shown prices in USD always however the amount randomly changes on page reload for specific games such as The Witcher 3 expansion. Apparently their webserver properly identifies my IP address as being Canadian sometimes and not other times, so I sometimes get the Canadian USD price (which is lower) and other times get the American USD price which is higher. They have no idea why this happens so they can't fix it, and I never know if the price I'm seeing is the right one so unfortunately I've had to avoid buying stuff since it has been happening until they fix it.

Im not actually seeing what the problem is here. It charges in dollars... and... Every time iv purchased in dollars it has been cheaper. I'm not complaining.

Switching currencies does just that, switch currencies, not prices. You won't get the USA price by switching to USD, but you'll simply get your price converted to USD. Of course, GOG's conversion rates are updated only every once in a while, and may as such be both better and worse than your bank's conversion rates.