Is it possible to have something like a DApp to find the closest Ether owner to purchase or sell ether?
Something that can be used as a decentralized market.
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It is possible to create a decentralised broker Dapp (it helps buyers and sellers find each other, but does not take part in the transactions and does not bear settlement risk).
Creating a decentralised market where USD or EUR or other non-ethereum currencies are involved, requires trusted escrow(s), who accept participants money in USD and EUR and promise only to release to another party at a signal from the Dapp. Or alternatively it requires trusted gateways (like in Ripple) that convert USD and EUR to equivalent tokens on the blockchain and back. Trust towards an escrow or a gateway is not the only concern. Escrow and gateway operators themselves are exposed to the risk of fraud from the market participants, because USD or EUR bank transfers or credit card payments can be reversed, if a fraudster claims to himself being defrauded.