If they pay by transfer they can charge back, the bank might cancel for some credit reasons, might flag it as they want to verify first why it was made, and so on. Cash is problem free if you live in a low crime area.
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.
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.