Maybe this is clearer?

> Imagine if I handed you a $100 bill and asked you to examine it carefully. Is it real money? Perhaps you immediately suspect it is counterfeit, and subject it to stringent tests. Let’s say all the tests pass. Okay, given that it is indistinguishable from a legit $100 bill, is it therefore correct and ethical for me to spend this money?

This "hypothetical" happens thousands of times a day at any retail outlet that accepts cash" - the cashier is handed a $100 bill, they carefully inspect it, and if all the tests pass, they accept it as a legitimate bill.

A single additional $100 bill is meaningless in the grand scheme of things. I have already accepted hundreds of them in my life time - why should I feel any ethical concerns about this?

So, yeah, when the tests don't work, that's okay? Or at least, it's not my problem. There's government agencies that deal with this, but the ethical issue is with the person making the bills and the obligation to act is on the government agencies. I have absolutely no obligation, and this is an established cornerstone of society.

Whatever supposed "hazard" you have in mind is one that society is already dealing with, on a regular basis, and... again: society has not collapsed simply because retail shops accept cash