It's an exchange where price discovery happens and there is no manipulation happening over there. I'm sure that Coinbase as prestigious as they are monitor trading activity closely every single second they are operational.
If there is any manipulation (which is very difficult to actually prove), it's likely happening on non regulated shitcoin exchanges that do not have much weight in terms of price discovery.
The pumps and dumps we see are normal considering that there isn't much that backs up Bitcoin and other cryptos value wise. It's all speculation where making money is the main incentive for people to be here.