I had a transaction reversed due to being 'high risk' as well.  I emailed support, and it took a week for them to get back to me, but the support guy said that he put me on the whitelist so that it doesn't happen again.  After that, I haven't had any problems and have the instant buy enabled now too.  The nice thing about the instant buy is you don't even have to wait for the buy transaction to be confirmed and they post the btc in your coinbase wallet to use.  I've sent them out to other wallets before they were ever confirmed and haven't had any issues.