Can confirm that it takes a lot of discipline to take negative reviews in stride. I give a lot of flack to the brands who threaten to sue, but when you get a bad review, and you're in a small business like that, it can feel as though you've been served an eviction notice from your life as you know it. You don't know how much that review is going to cost you in sales, but for a moment you feel like it might cost you all of them.This just goes away, like most such threats. Can you imagine either side settling or going to trial? The appearance of an NDA (review taken down or changed to the positive) would arguably be more damaging to the company. Alternatively, how can they prove cause-effect damages? An increase in CPI or a bear market is likely to be more impactful. Plus, it will cost them a truck-load of DACs to prosecute (well, maybe a pallet).
However, having been a brick/mortar/online business owner in the past (with absolutely everything on the line) I can absolutely understand how emotions may compell a business owner to want to go for the throat.
I know the feeling, it can seem a LOT worse on the other side.
That's really no excuse, you have to take a deep breath and be rational about it. What's really blameworthy is not being able to put the brakes on your irrational impulses even over the course of weeks or months.
What these folks should do is take the common advice: Write the angry email where you threaten to sue and burn their house down and all of that... then delete it and move on with your life.