I’ve sold a few things here. At least twice watches have been relisted within weeks for more money (one example for almost €6k when I sold for <€4k). I agreed to the selling price, so good luck to them if they think they can get more.
I had zero emotional attachment to those watches though. They were both bought well, sold at a bit of a profit, and had been on the sales forum long enough to have had good exposure. I wouldn’t give a monkeys if the buyers had made a song and dance about how much their new purchases meant to them. I only care about being paid, and very importantly a low risk of fraud as the expensive one was paid for by bank transfer.
But I do have a few watches that I’d feel pretty disappointed if they were sold to a “collector” only to be flipped. In these cases I would see deception in buying practices as being completely unacceptable. Other than that I don’t see what people can complain about.