At least in the UK, they might not accept it. I believe there is a limit to what you can spend in cash at places like car dealere, art houses, jewellers etc. I believe it's about £9000.

Meh... they'll secretly get upset with you. Plus it is much smarter to pay for it with a credit card and then pay the card off. That way you can get those sweet sweet rewards points...

from what i've seen they get unsecretly upset with you and furious that they are not getting their kickbacks for making you take out unnecessary loans

you can only stuff about a mil into a briefcase, rich people won't handcuff themselves to a measly mil