The Middleman for Ethereum

The buyer sends the money, give in required documents to the Middleman for validation.

Either the seller or Middleman can create a new contract. Only the creator can set the price information, and the fee for the Middleman.

When selling an item, usally the realtor will do the Middleman's role so the realtor will create the contract from hise/her PC, set the seller information (Etherum address) and the fee the Middleman will take from the price. Or a seller can create a new contract, asking somebody else like lawyer do the Middleman's role. The seller can set the information of the person doing the Middleman's role, his Ethereum address fee and the fee to that person.

The Middleman is the validator, and the witness of the contract. In the earlier stage of selling, the Middleman can check all the documents the seller or buyer give in (like, the history of the house, insurance information, inspection report, etc). This is 'Validated' state.

At the end of the contract, the buyer sends the money and once all paper process is done (the Buyer is now officially the owner of the house, for example), the Middleman confirms it. Only after that, the money is sent to the seller, and the given fee is sent to the Middleman. Now the contract is 'Finished' status, which means it's completed.

There can be multiple buyers for an item (like music), but the actual money transfer happens only when the Middleman confirms all document and item transfer is complete. That is when the Middleman hits the 'Confirm transfer of item' button.

Only the Middleman can cancel the contract if there's any fraud found or any of the seller/buyer don't want to continue. If the contract is canceled after the buyer sent the money, the money is safely returned back to the buyer.

You can also create a contract that doesn't required the Middleman. If you the contract doesn't require the Middleman, the purchace happen right away the buyer confirms the purchase. The money will be sent to the seller directly.