https://www.elfa.se/elfa3~se_sv/elfa/in ... geSize=100

Some of them aren't that expensive (the cheapest ones aren't MX, just keep that in mind). They are all sold new, and these I find somewhat interesting:
https://www.elfa.se/elfa3~se_sv/elfa/in ... &toc=20705
https://www.elfa.se/elfa3~se_sv/elfa/in ... &toc=20705
https://www.elfa.se/elfa3~se_sv/elfa/in ... &toc=20705
https://www.elfa.se/elfa3~se_sv/elfa/in ... &toc=20705
https://www.elfa.se/elfa3~se_sv/elfa/in ... 5-56&toc=0

I live close to one of their stores and don't have to pay any shipping. Anyways, just a tip if you ever want brand new ones, it is an option, although quite expensive still. Their site is available in several languages and currencies btw.

I quite don't see, what's so great about these keyboards / this store.

At least for people outside of sweden it's not such a great deal. Many of these keyboards are available for less in Germany.

btw. the keyboards you linked to are mostly Cherry ML keyboards, only the G80-1800 is with MX switches.

Edit: e.g. a G80-3000 LQCDE (with MX Clear Switches) can be bought for 49,95€ plus shipping in Germany, while at that store a comparable keyboard (G80-3000LQCEU) costs 761 kr (90,15€)

None of the G80 keyboards are in Swedish layout. There is only EU, CH (Swiss) and DE (German).

I though more of them were actually MX and not ML too, so it wasm't that good at all.

It's really easy: G80 means Cherry MX. G81 means Cherry MY. G83 and G86 means Rubberdome (G83 are customer boards, G86 are Point of Sale). And G84 means Cherry ML.

Only G80 keyboards have MX switches. (But knowing which kind of MX is a lot harder, you need to look at the Suffix for that. On modern USB G80s XPXXX means blacks, XSXXX means Blues, and XQXXX means Clears. I don't know about non USB ones exactly, but XAXXX definitely meant Blacks. I think XFXXX are blues, but I'm not quite sure. The same with the old three letter Suffixes.
Then the first letter tells you about the keycaps. LXXXX means lasered, SXXXX means dye sub, HXXXX means Double Shot, and PXXXX means pad printed. The suffix behind the five letter suffix (insert xzibit pic here) tells you about the color. XXXXX-0 is gray/white XXXXX-2 is black. This can also tell you about the material of the keycaps:
ABS: all Doubleshots, all Pad Printed
PBT: all Dyesubs, all white/grey lasereds
POM: black lasereds

And the last two letters tell you about the Layout.

Everything you need to know about Cherry Boards.

There is a Cherry product codes wiki article with the same information, and more.