They also have had to incur some kind of damage as well. If someone says something mean about you, you can't just expect money for that. It has to have harmed you in some way- like getting kicked out of your apartment or customers cancelling orders/sudden drop in customers after the action.

I think proving a review actually lost them business might be tricky(I guess the seller would have to go with: buyer posting negative review = foreseeability of damage to their business?).

I dunno how it would affect them trying to prove a breach, which would likely only get them their suit/time spent drawing the artwork(and that'd need to be priced, there's more fees) back- not damages.

I dunno on this one. *L* The American laws on it in this case are way different from my country! And I would have assumed Free Speech would protect this kind of things, I'm kinda shocked it doesn't.

I live in a common law country where we have both the legal fiction regarding unfair terms and the Unfair Terms Act itself and these tend to consider trying to ban a fair review of a product as an unreasonable term. So the seller could never win trying to enforce it as a breach.
(NDAs, as were mentioned above, are not considered in the same kettle of fish as a review by the direct/end consumer)