In the US, admitting you did something wrong could open you up to a class action suit where some customers could be eligible for damages due to negligence.
You and others assume the merchant is unscrupulous, but they provided a remedy, so when you then called them out on it and gave them bad PR, you’ve given less incentive for other businesses to provide even that.
You could’ve written your post without specifically mentioning the merchant’s name, if your intent were really only to help others.
Even worse, if the merchant were unscrupulous and your aim were revenge, if it were to turn out that the merchant gets more business because of the PR around your stunt, they might tell other unscrupulous merchants that they should not pay their agents and hope for a windfall from rewarding only one of them with their due.