I feel like "the customer is always right" is one of the most misused sayings out there... like, in spirit it's a reasonable reminder for sellers to not argue with the customer. But instead people take it as some proof of epistemic truth on the level as "they say that the Earth is flat. They're a customer, so the Earth is flat."
This too. But I wouldn't call it more cynical; it's simply that you don't know how the goods are going to be used as well as the customer does, so from their PoV what you consider buying something dumb might be actually smart.
It should really be considered more as "the customer is always right in matters of taste".
But even that goes so far. I once had a lady try to buy kids ski goggles that were too small and blocked her vision because she didn't like how big adult-size goggles are. I refused to sell them to her because that is dangerous to other people.
Right. That's my point. To her, the way she looked was the only thing that was important and she refused to accept the reality that kids goggles were a danger.
When I worked retail, the owner told a different version, "the customer is always the customer." (Silly sounding I know). The thought was they weren't always right and you definitely didn't have to do what they said, but you should always treat them with respect. Even when they or their kids were being twats.
"Blood is thicker than water" is up there. The full saying is "the blood of the covenant is thicker than the water of the womb" which means that family isn't the most import thing.