The customer will never care that the transaction is delayed into the blockchain (delayed until the cartel's mining servers wins a block in the proof-of-work), because Amazon will give their customers 0-confirmation access to what they purchased.
So that delay is irrelevant.
Amazon won't care about it?
Sure, Amazon can trust its customers not to double-spend. But so can all the other merchants.
I already explained this upthread!
Customer would be banned from all cartel member sellers after one double-spend. Not very wise for the customer if the cartel is widespread in retail and online.
Also most purchases (not downloaded) ship after hours, so if the cartel has 15% of the network hashrate, any double-spend would be detected before shipping.
There is no way that this cartel starts with anything near 15% of the hashrate.
Disagree.
Even if so, 1% of the hashrate means the spend will be in the block-chain before it ships in most cases.
And even if not so, that is irrelevant because the customer will want to buy from the cartel again and not lose reputation.
Besides Amazon doesn't sell to those who don't provide a name, address, and credit card (i.e. some form of ID), thus they can send the collection agencies after you.
To argue that a cartel can't invoke the powers of the law against fraud is nonsensical.
As well to argue that a cartel can't issue 0-confirmation transactions is nonsensical, and this is a good thing for Bitcoin since the 6-confirmation time is 1 hour.
P.S. Tangentially to argue that a cartel which controls 15% of the online transactions (by value not quantity) can't control on the order of 15% of the network hashrate when mining will be solely funded by transaction fees is also nonsensical.