There needs to be an additional deposit amount paid by the buyer and determined by the seller.  Once the transaction is confirmed by both parties, the buyer gets this amount back.  This ensures that both parties have some "skin in the game" that motivates both to confirm that transaction.  This will eliminate any extraneous impulse of the buyer to simply never confirm the transaction.

Actually, now that I think about it, there should probably be a seller's deposit as well, to ensure he actually sends the product.  The buyer and seller deposits make it a bit more complicated, but they ensure everyone is motivated to conclude or mediate the transaction.

If you think about the three scenarios...
Current proposed:
1. Buyer puts up the money, seller delivers product. --> Both happy, price goes to seller.
2. Buyer puts up the money, seller does not deliver product. --> Buyer's money is destroyed.  Seller doesn't care.
3. Buyer puts up the money, seller delivers product, buyer doesn't confirm product. -->  Seller doesn't get paid.  Buyer doesn't care because, to him, he's lost the money either way.

With Buyer deposit:
1. Buyer puts up the money, seller delivers product. --> Both happy, price goes to seller.  Buyer's deposit returned.
2. Buyer puts up the money, seller does not deliver product. -->  Buyer's money is destroyed.  Seller doesn't care.
3. Buyer puts up the money, seller delivers product, buyer doesn't confirm product. -->  Seller doesn't get paid.  Buyer remembers deposit, completes/mediates deal.

With Buyer and Seller deposits:
1. Buyer puts up the money, seller delivers product. --> Both happy, price goes to seller.  Both deposits returned.
2. Buyer puts up the money, seller does not deliver product. --> Buyer's money is destroyed.  Seller remembers that his deposit is on the line, deliver's product.
3. Buyer puts up the money, seller delivers product, buyer doesn't confirm product. -->  Seller doesn't get paid.  Buyer remembers deposit, completes/mediates deal.

Both deposit amounts should be equal, for simplicity and also to ensure that the seller, who is listing the products by both price and deposit amounts, is doing so fairly.