When I bought a piece of furniture in Germany, I had to pay 1/3 right there in the store. They accepted various cards. When it was delivered, I had to pay the remaining balance (four digits) in cash. No other option.

Also, I believe when buying used cars and such, most people still prefer cash transactions.

That's pretty common in the US too though the cash balance is usually in the form of a check. Historically you'd often get a cashier's check from your bank but I was surprised the dealership accepted a regular personal check a couple years ago. I guess there are control systems in place these days that provide assurances for places like dealerships.

For a dealership I feel like there's less risk; they can do a quick background/credit check on you before accepting the personal check, and it's probably easier for them to track down someone who gives them a bad check. They also have better ability to absorb the loss, in the worst case. I'm sure they've modeled everything and have decided that taking personal checks is worth it financially to them.

(I remember reading long ago that if if a potential customer has to leave the dealership to go secure the proper form of payment, a significant percent just don't come back at all. They want to keep you there until you buy something, fairly standard sales tactic.)

But for a regular person just trying to sell their own car directly to someone else, they're absolutely going to want a cashier's check or cash. (Even the cashier's check can be risky; I doubt your average person is an expert in detecting a fraudulent one.)

When I’m selling a car I insist that we finalize the transaction at a brick and mortar bank, where I can watch them either get a bank draft or withdraw cash.

(In Canada, I’ve never actually seen a certified/cashier’s cheque used for anything. My house downpayment and vehicle purchase were both done via bank draft.)

and even if you do want to carry that much cash, surely you'd want a fatter wad with smaller bills, right?

The Euro uses larger bills for larger amounts, so if showing off the cash is actually something you want, a single €500 note would have worked well.

there's a psychological bonus for heftier things

maybe if it was larger, thicker, and a more dense material. most of those matter more to the person holding it, rather than an observer, though