A less risky solution would be to have a blackout period equal to something like the same account being unable to place new orders for 30 seconds (minus the amo

A less risky solution would be to have a blackout period equal to something like the same account being unable to place new orders for 30 seconds (minus the amount of time the order was in the market) after cancelling an order. People make mistakes and you need to let people get out of the market quickly if they do. (People mistakenly transpose the price and quantity more often than you'd expect, etc.) Having a forced cool down period after placing a short-lived order reduces the impact of these sorts of orders without increasing the risk of mistaken price/quantity/side. I'm not sure if coinbase allows amendments of quantity and price on existing orders, but they should have similar time restrictions on amending up the quantity or amending the price to be more aggressive following a quantity amend down or price amend more passive.