Q. When a distant store had a sale on tuna, I made a special trip to stock up. But when I arrived, they showed me the fine print of the ad stating "limited quantity." Shouldn't this have been more prominent?
A. A well-known Talmudic discussion will provide the precise answer to your question.
Nowadays we know if the meat bought in a supermarket is kosher by the stamp of the supervising agency. But in the time of the Talmud, most meat was sold fresh and unpackaged. One method of "kosher certification" was to announce to the public any day there was any unkosher meat in the stores; the kosher customer knew not to buy meat from a regular store on these days.
The question arose how to word this announcement. The most effective way would be something with punch, like "Carrion today!" But such an offensive description would deter even non-Jewish customers who ordinarily buy non-kosher meat. Conversely, if the wording is too subtle it may fail to get the message across; then the customer is being misled.
In the end the agreed-upon wording was, "Meat for the soldiers today!" Any reasonable customer would figure out that meat for the soldiers in ancient Babylonia was probably not kosher; the Talmud tells us that if there are isolated individuals who can't figure this out they have only themselves to blame.
We can make a direct parallel to your case. The most effective way to communicate the quantity limitation would be to boldly state, "Up to six cans at a bargain price!" But this description bears an air of stinginess, which could put off the customer. At the other extreme, a vague statement like "Some restrictions apply" is just too vague. What is called for is something that is adequately informative for any reasonable consumer.
If the vast majority of those seeing the ad would suspect a quantity restriction (after all, these are fairly common) or would be likely to notice the fine print, then the merchant has taken reasonable means to inform the consumer without blunting his message. In this case, you have only yourself to blame for your haste. But if there is a significant minority of readers who are likely to be misled, then the merchant hasn't properly fulfilled his responsibility to be open with his customers.
The exact adjudication of such a case depends on the details of the case. How common are quantity restrictions in your area? How sophisticated are the shoppers? How small was the fine print? And so on. But the basic criterion remains the same: any substantive limitation in the advertiser's product has to be communicated in a way that is understandable to the large majority of reasonable customers.
SOURCE: Babylonian Talmud Chullin page 94.