The paying with coins case

Was almost 20 years ago

Buying new cars is in fact a pretty lousy way to launder money for a variety of reasons, but the main one is that new cars depreciate rapidly. When you convert you new car back into now-legitimate cash, you end up with considerably less than you paid for the car. A crim who buys a flash car isn't doing that because he wants to launder money; he's doing it because he wants to have a flash car.

Generally the preferred way to launder money, if you have a regular supply of money needing laundering, is to establish and operate a basically legitimate business of a type that handles a lot of cash anyway — often a retail business. Over time you add your ill-gotten cash to the till and record it as takings of the legitimate business. You pay tax on it, of course, but you can generally arrange matters so that the legitimate business is not that profitable, so doesn't pay a lot of tax. And paying the tax is just part of the cost of laundering the money, so far as you're concerned.