Coinbase is ripe with asymmetric slippage and requotes, two very large red flags and HUGE signs of manipulation.

IF bitcoin was regulated in the USA by something similar to the SEC/NFA/or CFTC then this would bring audits, lawsuits, and eventually large fines and possible closure of the company.

It has happened to me as well, 3 times on the buy side and once on the sell side. Smaller amounts then you are mentioning here but still complete and utterly BLATANT market manipulation.

Cheers,