That is called a multisig transaction, but then what if the seller and the escrow are the same person? Then that does nothing since he can still scam.
how would that work if escrow colludes with one of the parties?
which is what appears to have happened with Master-P and a few recent transactions
If the seller and the escrow agent are the same person in 3-of-3 MultiSig transaction (buyer+seller+escrow agent keys), scammer will need the third (buyer) key to own the funds.