I've been on coinbase for a while, and up till now, they've pretty much been in lock-step with Bitstamp for current buy prices. Suddenly they're asking about + $30 per coin compared to Bitstamp and Bitpay BBB prices.
When the price was at 690 on Bitstamp and I was considering buying another coin or two, Coinbase was asking 720. Then about an hour into that, there was a huge buy on Bitstamp, and suddenly the Bitstamp prices 'was actually' 720. Now the Bitstamp price around 718 and Coinbase is asking 748. Still a $30 dollar spread. What's up with that? They're very cagey for answering inquiries on how they set their price, giving vague answers and not aswering more pointed questions.
I guess I'm not really complaining if they're manipulating the market in the up direction.

Though it would have been nice to pick up a coin or so at the actual low of 690 a few hours ago.