Coinbase only allows you to sell directly into your Coinbase fiat wallet. However, there is no limit on the amount you can sell to your wallet. After selling to your Coinbase fiat wallet, you can opt to either withdraw funds to your US bank account or repurchase cryptocurrency on the platform.
To sell cryptocurrency:
Select the Trade button
Select the crypto you want to sell and have it sell to your USD wallet
Then select your USD wallet and select Withdraw
When initiating a withdrawal of a sell from your fiat wallet to your bank account, a short holding period will be placed before you can withdraw the fiat from the sale. Despite the hold period, you are still able to sell an unlimited amount of your digital assets at the market price you desire.