The review system in place is set up as a one to five star rating system, with one being the worst, five the best.
In the past, we allowed users to give zero stars as a rating, but 90+% of the zero star reviews were actually people who forgot to enter a star rating with their review. We got tired of messaging people to tell them to go back and edit their reviews to correct the oversight, so we’ve switched to this format.
Really, it’s not much different. Adding a zero star would not be any different than making it a one to six star system, which nobody clamors for. If you really think the place is lousy, enter your one star review knowing that it doesn’t get any worse than that, and nobody is going to confuse your decision with forgetfulness.