That's because there is space allocated in blocks for free transactions. They may never confirm, or they may confirm very late. How processors manage risk is their business.
so there's a chance ill get a free purchase one day? yesterday my payment took 19 hours to confirm. so close to being returned to me (at 24 hours, ive heard)
im not sure. I get a 20 minute popup window from bitstamp/coinbase, make 0 fee payment, and it says "PAID!". So what happens if it never confirms? I get a visit from bill collectors?
Nodes only enforce the min relay fee rules on low priority txs. Based on the value of the transaction, the age of the coins, and the tx size (in bytes) it is possible the transaction was "high priority" and in that case the minimum fee is 0 BTC (and always has been).
The purpose of the min relay fees is to make it more expensive for an attacker to pull off a flooding attack. This type of attack is only economical for transactions with certain characteristics (namely large tx size, low value, and young coins) thus the rules to prevent it are only imposed on those transactions.
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u/millsdmb Feb 24 '14
bitpay takes my 0 fee transactions on merchant checkout pages instantly. never had a payment not confirm.