if you, say, pulled a couple hundred grand out of your pocket to buy a house that the sellers would trust that it’s real and above board even if it were?

Well it says exact "change" so I think yes if you dumped a few hundred thousand $1 coins out of your pocket when it's time to pay they'll think it's sus lol

I suppose though if they refuse it you've already generated it and can scoop it up into a wheel barrow and see if a bank will take it. They may not care about the coins too much but they'll definitely be reporting a guy bringing in a few hundred thousand dollars in coins every now and again to the IRS.