Wow. How far back can you go? I think if you want to find price manipulation, you probably need more than a few days of trades. Also, pick the days with highest volumes (2/5 - 2/6 is one that comes to mind).
I looked through a few of the highest volume traders. Even though it shows a lot of trades, according to the timestamp, the trades (for more than 1 trader) happened at the same time. My guess is GDAX list them as separate trades, but it really is just someone putting a very large single trade. I’m thinking of this scenario:
Seller A sells 0.02 BTC at $8500
Seller B sells 0.01 BTC at $8500
Seller C sells 0.1 BTC at $8502
The buyer puts in a taker trade for 1 BTC, and GDAX fills that trade from Seller A to C (and a whole bunch of others) to fill the order. Even though seller C is selling at a higher price, the buyer made a taker trade and bought at market price (best price available), which included seller C’s order. In the data you pulled, even though Buyer placed 1 trade, it looks like he placed a bunch of trades because GDAX filled it with multiple sellers, so it looked like he traded multiple times.
That’s my understanding. Love to hear your thoughts on this.