There should be a zero star option. I transferred enough eth for fees and another coin to use to trade in order to buy something not on the coinbase app. The trade function has never once worked. It either says you fine have enough to cover fees even if I have 5x more than the estimate OR more commonly it just errors out. Entirely useless. Just a bunch of fees moving coins around to accomplish nothing. And no support. This is a known issue they ignore.