I’ve done the same in the past when buying vehicles on my own with a pocket full of cash with no dramas, thankfully. Unless you’re a comic book Super Hero there’s not a lot you can do if they have firearms. Not bought A vehicle in a while now but would prefer bank transfer, in fact some sellers also prefer this because of fake bank notes.
Digressing slightly, when we sold my Dad’s Beemer after he’d passed away a guy came down from the Scottish Borders with £8k in £20 notes which I took straight down to the Bank while he waited which he didn’t mind doing. I paid the cash in over the counter so they could verify the notes which took them much longer then I expected. They were Scottish notes but fail to see what difference that makes to a bank! Then, about 10 days later I got a NIP through the post for a speeding offence on the A6 near Carlisle, 2 hours after I’d sold the car. A not so nice surprise for the new owner!