move 1 BTC from one wallet to another, third wallet pay for transaction?

[Carlton Banks]

If the child transaction is confirmed and included in a block, then the parent transaction would have to be in the same or a previous block as well.

right

Not sure about taint, maybe it won't, but do we know how companies like chainalysis works? Or do they use the same definition of taint as blockchain.info (.com) used to?

it's more about how actual Bitcoin transactions work, and whether this specific case (CPFP) segregates the inputs of the parent from the child.

[HCP]

it's more about how actual Bitcoin transactions work, and whether this specific case (CPFP) segregates the inputs of the parent from the child.

Well, given that the CPFP is simply spending the UTXO from a previous (unconfirmed) transaction (with a high fee), it's technically, no more or less "linked" than any other "normal" BTC transaction.

However, if one were to analyse the transaction fees of a given block... and possibly the "Received Time" of a transaction (such as displayed by blockchain.com)... it might be possible to identify CPFP transactions.

Basically, you'd be looking for the following conditions:
- 2 transactions in the same block (Transaction A and Transaction B)
- Transaction B spends UTXO created by Transaction A
- Transaction A has a "low" fee relative to current fees being paid by other transactions in the block
- Transaction B has a "high" fee relative to current fees being paid by other transactions in the block

Less conclusive indicator would also be looking for Transaction A to have been received several "blocks" before Transaction B... as theoretically someone attempting to do this on purpose could broadcast Trans A and then immediately broadcast Trans B.