If it's just a mistake then they are not bound to sell it for that price. Especially if everyone else can easily recognize it as a simple mistake of where the decimal is.
> The store must honor the price in the advertisement, even if it is wrong, until they correct the misrepresentation using the same advertising medium and/or by corrective signs in the store.
> Items sold in a grocery store must ring up at the lowest displayed price. Food stores that are in the waiver program must offer consumers one of the items free if it scans higher than the lowest advertised price.
[1] https://www.mass.gov/guides/a-massachusetts-consumer-guide-t...
Also, grocery stores sell a lot more than just groceries.
Does anybody reading the sign not understand what it's trying to communicate?
"It's a banana Michael. What could it cost, 10 dollars?!"
You say "obvious" but I don't think that means what you think that means. Why is it obvious? Why would it be impossible that a store sells bananas at a loss in order to pull people in (what people in sales call a "loss leader")? If you don't buy bananas regularly, why couldn't you assume this is just a great deal?
If there were a sign advertising 5 bananas for a penny (or whatever) with no asterisk, fine print, or mention that "terms may apply", I would be livid if I couldn't take advantage of that price.
If you would like links: Here's a 5 year old piece about Amazon giving away bananas: https://www.foodandwine.com/news/amazons-free-bananas-disrup...
Here's a 2 year old coupon for free bananas from some couponing blog: https://www.thecouponingcouple.com/free-bananas/
Another blog, more free banana coupons: https://spoonuniversity.com/how-to/10-food-budgeting-tips-i-...
TL;dr- Don't put up bullshit pricing signs and assume people will understand the "joke", you're coming from a place of different cultural awareness and it will burn you when people like me get involved.