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.
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.
I hate this fucking phrase, nobody understands it. It does not mean the customer in the individual sense, it means it in the sense of the market as a whole. As in if I have a store selling blue hats and many people keep asking me for purple hats, I should start selling purple hats.
The customer is not always right. When I worked in retail we were taught to always put the customer first, which was some bullshit about communicating with them in good faith. But they could be misinformed and therefore not right.
"The customer is always right" refers to the fact that demand can be inferred by what people buy. If you own a store and you're like "nobody is going to buy these bright yellow sweaters" but the bright yellow sweaters are selling like hotcakes, then you are wrong. People are buying those sweaters. And we call people who buy stuff customers.
Does it really, though? That's a common unsubstantiated claim on random forums but I've never seen any real evidence that that is the original phrase and not something that was later added. Edit: Though the addition probably is closer to the intended meaning, customers obviously can be wrong at times.