None of these examples nor discussion get anywhere near the core of acausal trade, nor the objections to it.
The core is that you don’t know anything about the so-called trade partner except that which is a priori deducible from your model of the wider universe, specifically from your model of how other entities in the wider model of the universe model acausal trade with things in their model of the wider universe.
Almost all posts about acausal trade talk about two entities, unable to directly communicate but able to specifically model each other, but this is misleading to the point of being an incredible lie. They don’t and can’t know anything about each other, and while they are generally supposed to be superintelligences and could model each other in sufficient detail if each was sufficiently well described to the other, there is no such description. There are immensely more possible entities for each to consider than atoms in the visible universe—too many for even a superintelligence to model accurately regarding their counterfactual specific decisions.
You know of nothing that has destroyed this civilisation, and you believe this provides sufficient evidence that a descendant of this civilisation exists today, one who would also send fifty dollars to your preferred charity if an apple were placed in the right spot.
No. Under this analogy, you definitely know that there is no descendant of this civilization that will send fifty dollars to your preferred charity if an apple were placed in the right spot. That would be causal!
All you know is that there might be any of infinitely many civilizations, with apple-spot-caring civilizations making up 10^-100 of them or less, and none of those apple-spot-caring civilizations know that your civilization exists, and certainly don’t know that you exist, let alone what your favourite charity is and whether you have placed or are likely to place an apple in that spot. It’s likely that half of them would instead donate to the Puppy-Kicking Foundation or worse if they did know, because they very much care about apples not being in that sort of spot (and don’t care about puppies).
You don’t know which is more likely, and can’t spend the brainpower to figure it out: they make up 10^-100 or less of the infinite distribution, and 10^-100 of your computing infrastructure isn’t even one atom-nanosecond and there are many much more important things to think about.
Humans are not ideal Bayesian reasoning engines with unbounded ability to track all possible hypotheses.
In principle an ideal Bayesian reasoner could deduce the hypotheses of life, resource competition, strategies for obtaining resources, and the possible existence of scams from basically nothing (in addition to myriad other hypotheses). If they’re starting from the existence of markets as implied by being able to understand the letter at all, they could get to scams almost instantly.