Maybe I haven’t understood your point but it sounds like you’re describing people both acting maliciously and being stupid about it., so I don’t see it as a case of Hanlon’s razor.

Exchanging the item for another one that’s cheaper, even if it’s only $6 total, is still dishonest. The fact that it may not even be worth it for them in the end doesn’t change the fact it was an attempt to mislead. They were listing a product, and delivered another one.