Are the prices listed? If yes, then it is willing seller willing buyer scenario. Premium prices listed, expectation determines satisfaction.
Two opposite sides to this that are more unethical:
~ extremely cheap prices, but way under-delivered. Example prawn noodle for $1, but no prawn at all. Misinformed buyer.
~ no pricing, aka 4 prawns for $80 at Newton. Mistake on buyer's part, but seller preying on lack of information cannot be deemed ethical.
In these two cases, it is not a willing buyer willing seller situation. A mis-informed or un-informed buyer cannot be considered willing. That's no different to conmen using magic stones or needle in the egg stories.....