This is a quote from the book "On Zero Confirmation Transactions" by Chris Pacia below a certain value, while ShapeShift continued to accept them.

The fact that ShapeShift failed to stay up-to-date with changes in miner policy, and paid a small price for doin
g so, is hardly evidence of unconfirmed transactions being ‘trivially double spent’ or ‘always unsafe’. Yet the opportunity was not missed to push that propaganda on everyone.

/> Replace-by-fee

Up to this point we have been considering a network where all miners are using the “first-seen” policy or variations thereof. In such a network, we can ...
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