Do you have any idea as to why it would be illegal? In my country it's not at all unusual to see a product in a supermarket being sold at a discount price in a display at the front of the store, but at the usual price on the usual shelf.

In France if two prices appear somewhere, you'd pay the lowest on request I believe.

My gut feeling is that A/B pricing would be illegal because it's unfair: a part of the buyers have a discount the others don't even know about.

IANAL though :)

How about gas stations? They routinely charge different prices for the same product from the same store?

Do you mean same brand or same physical store ?

I believe as long as it's a different physical store, it's probably possible to set a different price.

My impression (that would need more research) is that having two different prices for the same product at the same time inside the same physical store or on a website would be problematic; otherwise it's probably ok.

I think I really need to make more research - A/B pricing would definitely be interesting.

Not in my country they don't.

I'm not sure which is more common (fixed price across the country like here in Uruguay or Argentina, or store-by-store variation like the US/Canada)