It doesn't look like they canceled your order because the price went up, they canceled it because their internal risk models showed you as being a high risk customer. They likely do not take price into consideration when deciding if they are going to cancel a transaction as this would be negative to their reputation. With that being said I would highly doubt that a lot of people are going to be complaining that they canceled their order when the market turned against them.
No disrespect, but this is about the most lame answer I have ever seen. You can't accuse the customer being a risk in this case, the risk is all on the back of coinbase and them not wanting to take ANY type of loss that might be due to BTC price fluctuations . So they picked a business and want o limit their risk by screwing the customer, its that SIMPLE . if I put in a ACH transfer, and my bank accepts it the deal should be done . Its not like the customer didn't have the money . no where in this case do I see where the customer did not have the money or was declined by his bank. Simple answer, work local and buy BTC local via craigslist or something similar . This business model coinbase is using is from and era that has long since died .. Person to Person transitions is the best way to deal with this .
If coinbase did not properly manage their risk then they would need to charge a much higher spread to their customers. It is these risk models that allow people to buy bitcoin from them quickly and without having to pay a huge spread over other ways to buy bitcoin. If I had to guess they probably actually end up canceling more orders when the price is declining because people are most likely going to try to use their bank to get out of a trade because they have lost money.
