There are always concerns over anything but cash, but even with cash, you have to check each note carefully.
I've attempted to eliminate and derisk as much as possible recently when I've recently bought and sold cars.
It can get a bit messy (and dangerous) with having to carry large amounts of cash around, but I got around this by contacting the branch of my bank that was local to where the car was and arranging for the branch to hold the right amount of cash for me.
Use the drive to the bank as a test drive and if you agree the deal, get the bank to issue the correct amount of cash, get the other party to agree this, sign the necessary documnets (V5, receipt etc) in the bank and then its sorted.
You don't have such great issues of carrying cash around, you know the cash is good etc, etc..... and the deal will be done in full view of the security cameras in the bank should there be any comeback!! - Sorted!!