Why do prices for games offered on GOG are different for users that are logged in?

On the first screenshot I'm logged in and have a higher discount, but also a higher base price, which makes the game more expensive. In a private browser window (on the same PC!) the discount is lower, but the base price is also lower, so all in al the same game (or bundle, to be exact) is cheaper.

Also interesting - when adding the cheaper version to the cart and logging in, the cheaper price prevails. What is going on here? Do we have to start checking prices through private browsing to check if we really get the deal we "should" get? As a long-term GOG customer I do not understand why I am shown higher prices than someone who is not browsing the GOG store using his account.

You usually don't see different prices based on whether you're logged in or not.
You see different prices based on in which country you are, or better, in which country the shop thinks you are.

If you're from Germany, like your profile suggests, €2,99 is correct.
But if you're from Poland, you'd have to pay €3,09.

Why it makes a difference for you I can't say. Maybe your private browser mode uses some kind of VPN?
For me at least, it doesn't matter if I'm logged in or not or which browser I use.

Which price do you see here
€11,21 or €13,50?

Like HiasX said: your account shows Germany as your location, but you look at the Polish shop, so...what/where are you?

I'm a German in Germany, and if I look at the offer in all the different languages, I always see the same price.
Doesn't matter whether I'm logged out or logged in.

I live in Germany but speak Polish, that is why I use the shop in Polish. I am currently in Germany with no VPN active in my browser or my computer. Maybe this is some cookie stuff., I'll check it out.

When I click on the Divinity link I get the lower price of the game 11.21€ when logged in (could be because I already own it?), when opening the same link in a private session the pirce goes up to 13.50€

When I click on the link I get the €13,50 offer.
Doesn't matter whether I use a private window or not.