This is why it federates, you can find offers from other instances that are further away just fine. However to make curation easier and lower the server load the admin can limit the geographic distance of federation so that for example it doesn't have to federate thousands of posts from Japan that few of the users of their location specific instance are likely interested in.
I really don't understand why that is so hard to grasp conceptually and this is definitly good design.
Well, that is the difference between a centralized system like Facebook and a decentralized system like the Fediverse.
But why would you not join a Swedish instance that lists only Swedish offers when you live in Sweden and are interested in offers near you?
Flohmarkt isn't a social media site or a global market place for ordering cheap crap from China 🤷
How are you so widely misunderstanding how it works? There is an location specific instance that you join when you are interested in classified ads from that location.
This isn't a website like Alibaba for global sellers to market their products. It is a location specific classified ads page and works exactly like most of them do.
Why is it bad design that you have a location specific page where you post location specific classified ads? Thats how all of them work.
So you are only complaining that accounts are not centralized? The entire Fediverse works like that and I don't really see an issue with that.
And why would a host change the location for their "Classified site for Berlin" instance? That doesn't make any sense, since it is location specific by design.
I am not very familiar with how the seller part of ebay works, but as a buyer I have a country specific account that only allows to bid on country specific offers. At least it was like that when I used it last some years ago.
From the Craiglist site:
craigslist sites are based on geographic location
This is a map and list of our sites:
You can find the closest craigslist site for your geographic location by zooming in on the map or browsing the list underneath the map.
Please note that the site location for a posting cannot be changed.
You will need to start your posting over again from the beginning if you have chosen the wrong site.
It is not possible to post to more than one site at a time.
This sounds exactly how Flohmarkt works, exept that they have a convinient map for you to find the location specific site. This would probably be a nice feature for Flohmarkt as well as part of an instance chooser.
I guess what you are stuck up on is browsing listings, not posting them. But that is more like an intra-instance search tool similar to how there is the Lemmyverse search engine for Lemmy. But I find that of very limited use for a location specific market place like Flohmarkt, where you already know which location you are interested in and don't need a search engine or drop down box to confuse you with listing options from entirely different locations.
I think there is some talk about adding more fine grained location specific groups to Flohmarkt (a bit like Lemmy communities), that would probably also allow posting from another federated account into them, but that would likely be counter productive as it would dillute the explicit location specific focus.
This is like all the popular classified websites work. This isn't aiming to be a replacement for Amazon or Alibaba, but sites like OLX or Craigslist that are very location specific, just like Flohmarkt.
I can't post on a Mastodon instance with another instance account, only comment on people's posts. This is the same way Flohmarkt does federation.
I also can't create an community on Lemmy with an account from another instance.