But if they both are involved in a scam then they are the same owners right ?
What do you mean by "both involved in a scam"?
https://sharedcoin.com/ from their FAQ "How does it work?
Shared Coin is a method of making transactions which requires less trust in the service. Shared Coin is based on the CoinJoin concept which acts as a meeting point for multiple people to join together in a single transaction. Having multiple people in a transaction improves privacy by making transactions more difficult to analyse. The important distinction between traditional mixing services is the server cannot confiscate or steal your coins."
So one can share your transaction with someone you don't even know. Can you re ask?