I don't think there's anything you can call these "high-risk" transaction cancellations anything other than blatantly dishonest business. The company is getting an unfair advantage during 3-4 day swings in price where they can arbitrarily decide to cancel the ones that work out in the consumer's favor, while keeping every transaction that is "high-risk" to the consumer. Yes, they are growing and seem like the most reputable source to buy BTC in the US, but to me, behavior like this says a lot and raises a major red flag. I'd really like to see this issue get more exposure in order to correct this bad business practice.
It appears bitbook is doing something similar with odds changes. It's really a shame to see some of these bitcoin businesses trying to unknowingly squeeze extra money out of their customers rather than simply taking what is theirs for the honestly great service that they provide.
I really don't think this is the case... CoinBase uses an automated payment processor. If the withdrawal is approved, your coins have been purchased; if the withdrawal is flagged by your bank the funds will be held in a reserve account for an extended length of time before being released to CoinBase. It's not exactly like they just pick and choose who to allow to buy.
Chances are these "High-Risk" transactions are the result of the withdrawal being flagged as suspicious by your bank.
I'd agree with pungo on this one, bit wager, as in my case, I purchased Bitcoin at about $905 and, at the time of the transaction cancellation, it was down to about $750, but I received a full refund. So in my case it worked out to my advantage that the transaction was cancelled, but of course, my intention was not to try to make a quick tiny profit but to purchase some bitcoin...;o)