> What if you wanted to buy a $25,000 car in cash from a dealership?

I think you’ve not done this in the past twenty years, or just heard the phrase and misunderstood it.

“Paying cash” at a dealership for a new car doesn’t mean literally bringing in paper currency. Generally you pay via cashiers check or wire transfer (rarely via personal check, but with a waiting period most of the time then). Saying “paying cash” at a dealership means “not financing the vehicle.”

I’m not saying it’s not possible to use paper currency, I’ve done it myself. For anything of value though, you’ll generally get a less enthused recipient (as they’ll have hassles depositing it), not to mention the hassle you’ll get just to withdraw the money. As an example in the US, withdrawing over $10k in cash requires filling out paperwork. Withdrawing much larger amounts will generally involve even more scrutiny. Trying to break up the withdrawals to stay under $10k will very likely set off red flags with the bank and lead to inquiries from their compliance department at best (usually much worse).