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.
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