I already came up with a metaphorical situation to describe this, but I’ll make another.
You go to a bakery. You look at the menu. You see a cake on sale, priced at $5USD per slice. It says right on the cake that it’s $5USD a slice. You go to the register and purchase the entire cake, which is made up of 10 slices. (and therefore should cost $50USD) The cashier rings it up as costing $500USD and swipes your credit card before you spot this. In this hypothetical world, you can’t do chargebacks, refunds, or the like.
In this scenario, you say that the cashier did nothing wrong, that it’s the customer’s fault. That you can’t blame the cashier for lying about the price of the cake. That it’s the customer’s fault for not expecting the cashier to lie about the price of their goods. (because the average person is normally this paranoid about their daily financial interactions, right?)
This is a much more accurate hypothetical scenario than the one you put forward, since yours removes the agency of the guilty party (the squire/cashier), which has no basis in reality. The customer is responsible for how they use their money, but the producer is just as responsible for providing honest services. You don’t seem to comprehend the second part.

But I mean, if you’re ok with scamming people, you’re probably ok with being an asshol e…