They don't trust a smartphone app provided by their banking provider but they trust a random bloke they've never met with 10k in their back pocket. Right. Makes sense.
Scenario one - Person A bank transfers Person B $10,000 for their classic car at the car show. Person A leaves, and then several days later the money is clawed back from Person B's account as it turns out it was sent from a stolen/compromised account. They now have no money and no car.
Scenario two - Person A gives Person B $10,000 in cash for their classic car at the car show. Person A leaves, and Person B could give a shit about anything to do with Person A as soon as they are out of sight.
Scenario two - Person A gives Person B $10,000 in cash for their classic car at the car show. Person A leaves, and Person B could give a shit about anything to do with Person A as soon as they are out of sight.