There is always some sort of spread because arbing has fees, but 10-20% is unheard - had to be a momentary difference. I'm seeing $766 Kraken vs $789 GDAX right now. Both are easy to get USD in/out of* so pretty comparable.
* Before they started adding 50k/users a day and became so backlogged.
* Before they started adding 50k/users a day and became so backlogged.