Better yet; they have to have MORE prominent advertising with the retraction. At least a ratio of 1.5:1 for every ad they played on TV or radio and every billboard/print ad, etc. If they have to spend more than the initial ad outlay, maybe it’ll make them think twice.

Anything less is pointless. They can put out retractions, but the damage is already done for most of the people who heard/saw/read the original ad. Obviously it should involve a financial penalty as well (beyond the cost of running the retraction ads.)