Here's an article about spoofing and market manipulation of real money in regulated excanges: https://ankura.com/insights/spoofing-market-manipulation-and...
This quote from the above article, does not apply to crypto exchanges so far as I know:
"Rules govern how trading is done. Laws prohibit manipulative trading practices on both securities and futures exchanges."
"To date, no cryptocurrency exchange has registered with the SEC" from https://medium.com/semadaresearch/should-cryptocurrency-exch...
...Unless there's magically someone filling it just before they do (i.e. frontrun by an internal bot) every time they try. I have observed exchanges doing this. I don't believe that Coinbase is one of them, though, as others have pointed out with their positioning they are better of not to.
So how can they do this without getting caught (and they haven't been caught - firms like Alameda are watching closely)?
This sounds like one of those things that's easy to just exclaim but is lacking a mapping to anything specific