A car?
Suggesting laborious bureaucratic transactions over several days removes this common occurrence in that world, along with at many other gatherings of specialists - antiques, pedigree animals, whatever
If I send a 10k payment to someone via bank transfer it's in their bank account in 10 seconds. Maybe you live in a country where there are much harsher restrictions?
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.
I would not feel at ease walking around with 10k€
In fact I would find it extremely suspicious if someone told me it's their preferred method to get paid. I would totally expect a mugging.
I do myself all higher priced purchases in cash, even go to the bank and withdraw the money to go to the shop next door. For the same reason I use a VPN. My provider and my bank have no right know what I do or not do.
Would a certified check so the same trick?
Cash can be faked too
Cash can be faked but it has good anticounterfeiting features, unlike checks.
It's probably a good idea to have some reasonable amount of cash on hand for times when electronic payments aren't available for whatever reason (natural disasters, for example).