it all depends on the cost of the car, it can be quite difficult get the cash out, considering that a 20k withdraw could take up to 3 days notice and then they have to collect it from within the bank.
also deposit amounts above 10k could rrigger a suspicious activity report.
Also who in this day of age would want to walk around with over 10k in cash in their pockets, both parties would be scared of getting robbed.
On the flipside, who would pay that type of money for a car that they ain't seen in person? unless the car is uber cheap for what it is; some car dealers hire couriers to pickup cars from around the country; they are responsible for checking over the car and once it's OK'd the dealer does the transfer to the account.
Heck when I got rid of mine, some dude and his daughter pulled up, looked at the car and check that the log book was correct. confirmed my bank details and 2 mins later the cash was in my account, the car was on the back on the truck... and they was off.