Let’s imagine a world where time machines are invented.
Hypothetically, what’s stopping anyone from travelling to the past, where the dollar is much more valuable, and buying things at a much lower price? What if you then go back to the present, sell those things at a higher price and repeat the cycle? And wtf would happen if everyone there started doing that?
I think the most meaningful response is that effects on the economy wouldn’t be an issue because reality itself would break. Backward time travel would violate causality (cause and effect).
If you go back in time, even a microscopic alteration in events would lead to the universe being different than the one you came from in 2025, but how could you have come from the universe as it was in our 2025 if that universe never came to be because you changed how things would proceed when you visited the past?