Gathering the people involved till now in this #fediMarket question to create some impulse and general discussion about this topic.
This is not a proposal but some thoughts and unfinished considerations, looking for some input or to become at least some output itself.

As @thomas pointed out there is #flohmarkt, as it looks like coded by @grindhold@23.social .

It has apparently the goal to be all the contrary to a centralized system but aims to be more like a local give away, sales and advertisement platform. Actualy it's not an auction like platform, witch is quite an interesting take. Still looking thru the ccc-Media video presentation trying to get a grip on it. As of now I didn't get the local restriction. Not sure if the restriction is mend to be by IP of the users, the IP of the platform of users or just some kind of instance restriction.

The #GNUtaler discussion in this topic points to the general issue not only about payment but also about the system of trust that can be or could be implemented.
It is and was quite interesting to see how the #ebay concept didn't catch up in Latin America because there was way to much fraud and the only thing that could catch up was some kind of sales platform like #mercadolibre that actually turned out to become some kind of national advertisement platform for professional sellers.

What did tho work in an astonishing way, and let's please leave aside for a moment some issues bitcoin does involve, is the concept #localbitcoins came up with, actually as well as the famous #Silkroad example. Sites that managed to create some kind of trustless exchange. The particularity of localbitcoins tho was that they invented a reference system where people actually even meet each other and backed up their existence by some how proving each others identity. Ultimately the reference and reputation system of localbitcoins, reputation out of completed transactions and comments about them, as well as in person verification, created a functional working environment, something that till today is looking for a match out there.

All these a real critical issues. And perhaps not only for trade but to a certain extent for our #socialWeb, our #fediVerse itself. On one hand we have commercial transactions that can involve fraud and on the other personal information that also can be exposed to fraud and worth. In our decentralized setup this is even somehow more complicated as fraudsters can restart at any given moment from anywhere else, while at the same time reputation on mid and long term should and can matter.
So, what we do have is on one hand the "real me" function implemented for example by mastodon, and on the other we do have the signing capabilities of blockchains themselves. In particular of #electrum wallets, a decentralized wallet system that was created and is implemented not only by bitcoin but a lot more blockchains that want to show off with a real simple decentralized #FOSS wallet system.
To get this straight, this is not about any coin or acquisition of any coin at all, but the simple technical availability of installing a simple long standing proven decentralized FOSS software that has the capability to sign or prove the correctness of any kind of text string. Nobody needs to have a single cent of a coin, or connect to anywhere, to create a wallet and with it a wallet address that than can sign a text. In other words, any wallet address is an ID that can't be impersonated without the respective password.
So, it doesn't matter where for example the ID "bc1qp8xla8me0ykkh5wzrvkjgtdnuma0galep9cedu" as a profile name shows up, or which profile claims to represent the ID "bc1qp8xla8me0ykkh5wzrvkjgtdnuma0galep9cedu", unless it is able to show off with a text, for example:
"I do have access to the signing keys for this ID" signed correctly with that wallet address, that profile could be considered an impostor.

To create show cases for this idea, for this concept, there is on one hand the friendica fediVerse site:
inversion.tupambae.com/
The profile "blockchain" for example uses the just mentioned specific ID:
inversion.tupambae.com/profile…
as some kind of "none human readable address".

Than there is the site:
1dhfsbbdpv4wshuyc6197nymcfeqqk…
The subdomain name itself is a first generation bitcoin address that has been used on the web and even if the capital letter detail is not in use, references are found for example by google.
That site hosts a project profile that again uses a bitcoin #SEGWIT address as an ID:
1dhfsbbdpv4wshuyc6197nymcfeqqk…
Actually the bc1 segwit system is not case senitive, in other words no capital letters in those ID's.
That profile itself is a reference to a mastodon profile that uses it to claim it's "real me" identity as "btc SEGWIT verified":
mastodon.uy/@tierranietos

Again there is not only no need for to involve bitcoins or cents of bitcoins (satoshis) in this. Even bitcoin itself doesn't have to be used, as there are lot's of electrum wallets out there. They do tho only verify texts signed with the same coin wallet. There is for example a #namecoin electrum wallet, a first generation coin invented to create a decentralized URL system, as well as there is for example a #faircoin electrum wallet. Considering all the altcoins created out there, faircoin at least is/was an interesting option that apparently failed to a certain extent due to the intent or claim by some in the community to be tradable on exchanges.
Again, this is not about any coin at all but about the fact that we do have simple unique ID's at hand we can verify and we can use to create reputation and or invent some system of trust and reference on desktop and mobile.

Than there is the consideration of guaranties and identities in the middle that allow escrow as implemented by localbitcoins.
This escrow issue would involve somehow coins/tokens, at least as some kind of guaranty until the transaction is finished. Be it as a general input to prove the seriousness of an involvement, an offer or even a publication. In terms of bitcoin itself, the second level segwit technology allows the creation of circles of trust without even publishing transactions to the main bitcoin #blockchain.

@MagickVibia@pagan.plus
@norezervationz@tootworld.social
@thisismissem @annewalk
@resl @NGIZero

@jcbrand

It's been a few years now since #LocalBitcoins had added the requirement that traders must verify their #identity (#KYC) in order to #trade.

There is a handful of other #P2P trading platforms that are KYC-free though:

Person-to-Person bitcoin Trading Platforms
https://cointastical.github.io/P2P-Trading-Exchanges/