I didn't write "The difficult part is in correctly estimating which type of situation you are in." for nothing, and the hypothetical trinket vendor is just an example. Like you say, any situation where negotiating actually matters is unlikely to be about a one-time transaction.

That said, the GP comment was about trying to win the long game by sacrificing the short game, and I meant to point out that there is not always a long game and even if there is, not everyone subscribes to the same win/win philosophy and recognizing when your negotiating partner doesn't is a valuable life skill.