[Edited]. Reliable purchase/sell (also applicable for accounts) escrow scheme that motivates scammer to be honest to his trading partner (see discussion):

1. Before the escrow the buyer must have on the separate address of his wallet twice more coins than the goods costs (2x) and the seller must have on the separate address of his wallet as many coins as the goods worth (1x).
2. The escrow agent creates a transaction, according to which the buyer collateral & the buyer payment for goods (2x) + the seller collateral (1x) will be sent to the created from their public keys MultiSig address.
3. The buyer and the seller checks and sign the transaction, the transaction is broadcasted to the network.
4. After the transaction is confirmed, the seller sends the goods to the buyer.
5. The buyer receives the goods and informs the escrow agent.
6. The escrow agent creates the transaction, according to which the seller will receive the seller collateral & the buyer payment for goods (2x) and the buyer will receive the buyer collateral (1x).
7. The seller and the buyer checks and sign the transaction, the transaction is broadcasted to the network.

Seller is interested to send the goods to buyer because he can lose an amount equal to value of the goods.
Buyer is interested to release the funds after getting the goods, otherwise he can lose an amount equal to value of the goods.
Collateral will encourage both sides to be honest, and if something happens with the parcel to conduct a thorough investigation and find consensus.