[flignats]

Normally, yes. But if you sell it through coinbase and not gdax, cb let's you sell it instantly and acts as a buyer.

[coralreef]

How do you know they're acting as a buyer and not just creating a sell order on GDAX?

[flignats]

Because they just bought it from you at that guaranteed price. They could go and sell it on the market for more/less, but the price you sold it to CB for remains the same.

[coralreef]

That price changes dynamically at some interval, and is discounted against the trading market value, correct?

[flignats]

They do update that price frequently (minutes, maybe seconds) and there is a premium added to the price. I assume they add this premium so they can then go liquidate it for profit on the exchange as needed.

[coralreef]

That doesn't sound to you like they're just selling it on gdax?

[flignats]

They can do whatever they want with it after they have sold it to me for a fixed price.