I mean theoretically, sure. Realistically, no. Because people would reneg on their offers, and you have no recourse as a seller.

We could start a buy/sell/swap space using existing Lemmy technology, if we left the messy details for users to figure out foe themselves.

Messy details add up quick, though. Payments, currencies, mailing addresses, reputation, conflict resultion, returns, scammers.

But “Craigs List” solved basically none of that on day one, and went on to be pretty successful.

So it’s possible.

You mean as in an auctioning platform? That’s legally a bit harder to achieve, as auctions usually have the rule that if nobody outbids you, then your offer is binding. To enforce that, instances would need to verify your identity. That’s easy for a larger company to do, but not that easy for hobbyists.

And then, to be federated, you would also need to make sure that other instances that you federate with uphold that standard.

Also, if you do auctions across international borders, how do you even prosecute somebody who does not obey the rules of an auction?

My understanding is federated “payment” systems are difficult. I think there is active discussion on the topic, but I’m not sure where code/development is at, or if it’s even started.

I think flohmarkt ("federated decentral classified ad software") is the closest we have right now. It has low (~10-30) Monthly Active Users (MAU), but is in active development.