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It doesn't matter the age of your wallet. Without waiting for other blocks to write your payment you run the risk of a double pay leaving you with nothing. e.g. I buy some coffee and then immediately send all funds from that wallet to my other wallet. If the 2nd transaction gets recorded first, the first tx won't happen.

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This requires colluding with a miner, since nodes will reject a transaction that spends the same output as a transaction they've already seen. For a small payment like a coffee, it should be enough to check that the transaction has a reasonable fee and wait 1 second to see that it has propagated through the network.

The double spend problem with zero-conf payments is about equivalent to people making fake bank notes. It's possible and maybe a problem for small transactions (large TXNs people wait around for a few confirmations) but its stealing and just as illegal as any other form of theft.

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