If the two parties (the seller and the buyer) know about multisig wallet, they can make use of it. It can be 2-of-2 multisig in which the buyer and seller will open such wallet.
2 by 2 is risky for both cosigners especially for a large amount of coins. If anything happens to one cosigner then the funds are locked forever. A 2 by 3 is a better option.
In my example, Albert's 10 BTC are already in Bob wallet, but locked for X hours, unspendable by Bob.
If they are not in Albert's wallet, how can Albert spend them again?
I imagine the lock having 2 options: 1 - If nothing happen, the 10 BTC return to Al wallet. 2 - If Al lock is cancelled, Bob can move the coins.
If you are selling your house, you can sit around a table for 10 minutes before giving the guy your keys.
I understood your example clearly. All you need a third-party escrow who has very good knowledge about the industry that you are dealing and can make the right judgement about the deal before releasing or returning the coins back to the buyer.