Caveat Lector, translates to let the reader beware. I’m not sure the what that has to do with this thread.
Caveat Venditor, is pseudo legalese for let the seller beware, but it doesn’t mean that the seller needs to beware of the “real value” of the item for sale. It applies to the concept of real and implicit warranties. It requires the seller to “be aware” of what the buyer can rightly assume the product is warranted to provide. Which means that if I sell a product that a buyer rightly assume will provide some sort of ability or service then I as the seller must be aware, legally of that assumption. For instance, if I sell an aftermarket auto part (let’s say, a sun shade for a 2007 Pontiac Grand Prix) then that part must meet or exceed a reasonable expectation on the buyer’s part as to quality and reliability and compatibility. In other words: it’s reasonable for a buyer to expect that that sun shade fit in the windshield of the specified car and, you know, actually block the sun. And if it doesn’t, then I, the seller must be aware, the the buyer will expect satisfaction in the form of a replacement that does do those things or a refund.
As for the case you “cited:” there are plenty of reasons why a judge would uphold the sale. A judge’s jurisdiction in such a case revolves around whether there is a valid contract or not. If the buyer did not misrepresent themselves or the “true value” of the object, or cause, in some way, for that value to be hidden from the seller, then the the judge could determine there was no fraud involved and therefore the contract, and sale, were valid.
But, the op didn’t ask if the sale was legal, they asked if it was ethical. There’s often a lot of real estate between what is legal and what is ethical.